^^ 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


1.0 


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Lo    12.0 


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Hiotographic 

Sciences 

Corporation 


23  WKT  MAIN  STREET 

WEBSTER,  N.Y.  t45M 

(716)872-4503 


'^ 


CEHM/ICMH 

Microfiche 

Series. 


CIHM/ICMH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microreproductions  /  institut  Canadian  de  microreproductions  historiques 


Technics!  and  Bibliographic  Notes/Notes  tachniquas  at  bibiiographiquaa 


Tha  institute  has  attamptad  to  obtain  tha  bast 
original  copy  available  for  filming.  Features  of  this 
copy  which  may  be  bibliographically  unique, 
wliich  may  alter  any  of  the  images  in  the 
reproduction,  or  which  may  significantly  change 
the  usual  method  of  filming,  are  checked  below. 


D 


D 


D 
D 


D 


D 


Coloured  covers/ 
Couverture  de  couleur 


I      I    Covers  damaged/ 


Couverture  endommagAe 

Covers  restored  and/or  laminated/ 
Couverture  restauria  et/ou  pellicul6e 


I      I    Cover  title  missing/ 


Le  titre  de  couverture  manque 


I      I    Coloured  maps/ 


Cartas  giographiquas  en  couleur 


□    Coloured  inic  (i.e.  other  than  blue  or  black)/ 
Encre  de  couleur  (i.e.  autre  que  bieue  ou  noire) 

I      I    Coloured  plates  and/or  illustrations/ 


Planches  et/ou  illustrations  en  couleur 

Bound  with  other  material/ 
Reli6  avec  d'autres  documents 

Tight  binding  may  cnusa  shadows  or  distortion 
along  interior  margin/ 

La  re  liure  serr^e  peut  causer  de  I'ombre  ou  de  la 
distortion  le  long  dele  marge  intirieure 

Blank  leaves  added  during  restoration  may 
appear  withir  the  text.  Whenever  possible,  these 
have  been  omitted  from  filming/ 
11  <;9  peut  que  cetainaa  pagea  blanches  ajoutAes 
lors  d'une  restau  ration  apparaissent  dans  la  texte, 
male,  lorsque  cela  Atait  possible,  ces  pages  n'ont 
pas  At6  film>tos. 

Additional  comments:/ 
Commentaires  suppl6mentaires; 


L'Institut  a  microfilm^  la  mailleur  exemplairo 
qu'il  lui  a  4tA  possible  de  se  procurer.  Lee  details 
da  cet  exemplaire  qui  sont  peut-Atre  uniques  du 
point  de  vue  bibllographique,  qui  peuvont  modifier 
une  image  reproduite,  ou  qui  peuvent  exiger  une 
modification  dans  la  mAthoda  n(«rmale  de  filmage 
sont  indiquAs  ci-  dessous. 


Tl 
t( 


|~n   Coloured  pages/ 


Pages  de  couleur 

Pages  damaged/ 
Pages  endommagAes 


□    Pages  restored  and/or  laminated/ 
Pages  restaurAes  et/ou  peliiculAes 


\^ 


Pages  discoloured,  stained  or  foxed/ 
Pages  dAcolortea,  tachettes  ou  piquias 


□    Pages  detached/ 
Pages  dAtachtes 

[Tlf  Showthrough/ 
LJu   Transparence 

I     I    Quality  of  print  varies/ 


Quality  InAgala  de  I'impression 

Includes  supplementary  material/ 
Comprend  du  material  suppi^mantaira 

Only  edition  available/ 
Seuie  Edition  disponible 


T 

P 
o 
fl 


0 
b 
tl 

si 
o 

fl 

si 
o 


n 


Pages  wholly  or  partially  obscured  by  errata 
slips,  tissues,  etc..  have  been  refilmed  to 
ensure  the  best  possible  image/ 
Lea  pages  totalament  ou  partiellement 
obscurcies  par  un  feuillet  d'errata,  une  pelure, 
etc.,  ont  M  filmtes  A  nouveau  de  fa9on  A 
obtenir  la  meilleure  image  possible. 


T 
si 

T 

VI 

d 

ei 
b 
ri 
n 
n 


This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  documant  est  film*  au  taux  da  rAduction  ii^diquA  ci-dessous 

10X                           14X                            18X                           22X 

" ' "  ' 

26X 

30X 

y 

12X 

16X 

20X 

24X 

aix 

32X 

1 

i 
i 

B3 


The  copy  filmed  h«r«  hat  b««n  raproducod  thanka 
to  tha  ganaroaity  of: 


Douglaa  Library 
Quaan's  Univarbity 


L'axamplaita  fiimA  f ut  raproduit  grAca  A  la 
gAnAroaitA  da: 

Douglfis  Library 
Quaan's  Univarsity 


Tha  iLtiagas  appaaring  hara  ara  tha  bast  quality 
possibia  conaidaring  tha  condition  and  lagJbiilty 
of  tha  original  copy  and  in  kaaplng  with  tha 
filming  contract  apacificationa. 


Laa  Imagas  auivantas  ont  AtA  raproduites  avac  la 
plus  grand  aoin,  compta  tanu  da  la  condition  at 
da  la  nattatA  da  raxampiaira  filmA,  at  an 
conformitA  avac  las  conditions  du  contrat  da 
filmaga. 


Original  copias  in  printad  papar  covara  aro  fiimad 
beginning  with  tha  front  covar  and  anding  on 
tha  laat  paga  with  a  printad  or  illuatratad  impraa- 
sion,  or  tha  back  covar  whan  approprlata.  All 
othar  original  coplaa  ara  fiimad  beginning  on  tha 
first  paga  with  a  printad  or  illuatratad  impraa- 
sion,  and  anding  on  tha  laat  paga  with  a  printad 
or  illuatrotad  imprassion. 


Tha  last  racordad  frama  on  aach  microfiche 
shall  contain  the  symbol  — ^-  (meaning  "CON- 
TINUED"), or  the  symbol  y  (meaning  "END"), 
whichever  appiiea. 


Maps,  plates,  charta,  etc.,  may  be  filmed  at 
dl.*farent  reduction  ratios.  Those  too  large  to  be 
entirely  included  In  one  expoaure  ara  filmed 
beginning  in  the  upper  left  hand  corner,  left  to 
right  and  top  to  bottom,  as  many  framea  aa 
required.  The  following  diagrama  illustrate  the 
method: 


Lea  axemplalras  oriyinaux  dont  la  couvarture  an 
papier  eat  ImprimAa  aont  fllmAs  an  commandant 
par  la  premier  plat  at  an  tarminant  soit  par  la 
dernlAre  page  qui  comporte  une  empreinte 
d'impreaalon  ou  d'illuatration,  aoit  par  la  second 
plat,  salon  la  cas.  Tous  las  autres  axemplalras 
origlnaux  sent  fllmAs  en  commenQent  par  la 
pramlAre  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustratlon  at  en  terminant  par 
la  dernlAre  paga  qui  comporte  une  telle 
empreinte. 

Un  des  symboles  suivants  apparaTtra  sur  la 
dernlAre  image  de  cheque  microfiche,  selon  le 
cas:  le  symbole  — ►  signifie  "A  SUIVRE".  le 
symbols  V  signifie  "FIN". 

Les  cartas,  planches,  tableaux,  etc..  peuvent  Atre 
fllmAs  A  des  taux  de  rAduction  diff Arents. 
Lorsque  le  document  est  trop  grand  pour  Atre 
reprodult  en  un  seul  clichA,  il  est  filmA  A  partir 
da  I'angia  aupAriaur  gauche,  de  gauche  A  droite. 
et  de  heut  en  bas,  en  prenent  le  nombre 
d'imeges  nAcessslre.  Les  dfagrammas  suivants 
lllustrant  la  mAthoda. 


1 

2 

3 

1 

2 

3 

4 

5 

6 

VOLCANOES   OF  NORTH   AMERICA 


•:!M^° 


VOLCANOKS  OK   NOIMH    AMKKlt'A. 


li.il  Kii 


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\  Mh:    \\c-r^s  ni- 


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VOr.CAN'OES  OF   NOHTIF    AMKKH'A. 


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VOLCANOES  OF  NORTH  AMERICA 


A  READINa  LESSON  FOR  STUDENTS  OF 
GEoaUAFIIY  AND  GEOLOGY 


BY 


ISRAEL   C.    lU'SSELL 

PROKESSOH    (II-   (lEOLOOV,    UNIVKRSITY   OF   MKHIOVN 

Al'THOK  <.F   "r.AKI.S   UK   N„RTH    AMK1M..V,"    "OLACIEKS  OF 

NdKXH   AMKHICA,"    KTC. 


THE   MACiMILLAN   COMPANY 

LONDON:  MACMILLAN  &  CO.,  Ltd. 

1897 

AH  rights  renerred 


Q  r  ^,  o  ^   R 


/ 


Cor'VHKJHT,    IS'.lT. 

Bv  THE  MACMILLAX  tuMl'AXY. 


Nortnaotr  \9xtiB 

J.  9.  Cushinjt  &  Co.  -  Berwick  St  Smith 
Norwood  Mais.  U.S.A. 


/ 


INTRODUCTION 

In  the  present  volume  the  Western  Hemisphere  is 
considered  as  being  divided  into  two  portions ;  namely, 
North  and  South  America.  Central  America  is  included 
in  the  northern  division  for  the  reason  that  the  student 
of  vulcanic  phenomena  finds  a  break  in  the  volcanic 
belts  which  follow  the  western  borders  of  the  two  con- 
tinents, at  the  Isthnms  of  Darien. 

The  series  of  active  and  recently  extinct  volcanoes 
foniiing  the  major  part  of  the  "Windward  islands,  sepa- 
rating; tlie  Caribljean  Sea  from  the  Atlantic,  will  not 
be  considered,  as  it  is  most  intimately  associated  with 
the  geography  and  geologj'  of  South  America.  Although 
Iceland  is  more  closely  connected  geographically  with 
America  than  w^ith  Europe,  its  political  association  wdth 
the  Old  World,  and  the  fact  that  it  has  frequently  been 
described  by  European  travellers,  make  it  convenient  to 
omit  it  from  the  present  discussion. 

Among  the  leading  physical  features  of  the  southern 
prolongation  of  the  North  American  continent  compris- 
ing Mexico  and  the  Central  American  republics,  are 
numerous  still  steaming  and  recently  extinct  volcanoes, 
some  of  which  have  had  their  birth  since  the  Spanish 
conquest.  This  region  also  furnishes  examples  of  violent 
volcanic  eruptions,  one  of  which  is  probably  second,  in 


168787 


VI 


INTUODrCTIOX 


reference  to  intensity,  among  similar  events  witnessed 
by  civilized  man. 

Many  phases  of  volcanic  phenomena  occur  in  the  west- 
ern portion  of  the  United  States.  The  lofty  volcanic  moun- 
tains of  northern  California,  Oregon,  and  Washington  are 
among  the  most  beautiful  examples  (jf  their  class  to  be 
found  in  the  world.  To  the  eastward  of  these  giant 
peaks,  whose  fiery  glow  has  been  replaced  by  the  sheen 
of  snow-fields  and  glaciers,  lies  a  vast  lava-covered  re- 
gion, the  only  known  parallel  of  which,  in  the  extent 
and  thickness  of  the  once  molten  rocks,  occurs  in  north- 
western India. 

In  Alaska  volcanic  energy  is  still  active,  and  more 
than  a  score  of  volcanoes  have  been  in  eruption  since 
the  voyages  of  Bering  in  1725-30. 

It  is  the  character  and  history  of  this  vast  volcanic 
belt,  reaching  from  the  tropical  shores  of  Costa  Rica  to 
the  western  extremity  of  the  bleak  and  inhospitable  Aleu- 
tian islands,  that  the  attention  of  students  of  geology  and 
geography  is  here  invited. 

The  object  of  this  book  is  to  make  clear  the  princi- 
pal features  of  volcanoes  in  general,  and  to  place  in  the 
hands  of  students  a  concise  account  of  the  leading  facts 
thus  far  discovered,  concerning  the  physical  features  of 
North  America  which  can  be  traced  directly  to  the  in- 
fluence of  volcanic  action. 

It  is  hoped  that  the  accounts  of  volcanic  eruptions 
here  brought  together  and  the  discussions  of  the  accom- 
panying topographic  changes,  will  lead  the  reader  to  con- 
sult some  of  the  numerous  books  to  which  reference  is 


l.TKODUCTION 


Vll 


Bcl 

3t- 
11- 

i-e 
je 
It 
n 

a. 

it 
1- 

e 
e 


made,  aiul  thus  oljtain,  in  many  instances,  more  detailed 
information  than  it  is  practicable  to  include  in  a  bo«)k 
of  the  character  of  the  one  here  presented.  While  the 
facts  described  and  discussed  in  the  following  paces  were 
derived  in  many  instances  from  personal  observation, 
much  is  of  necessity  compiled  from  the  writings  of 
otlier.s.  In  all  cases,  I  think,  acknowledgments  are 
made  of  the  sources  from  which  information  has  been 
borrowed.  The  numerous  foot-notes  inserted  will  ena- 
ble the  reader  to  verify  the  accuracy  of  those  portions  of 
the  book  which  are  essentially  compilations. 

ISEAEL   C.  EUSSELL. 
University  of  Michioax, 
May  25,  1897. 


f 


CONTENTS 


IXTIIODUCTIOX 


rA(ii' 
v-vii 


CIIAITKH    I 

CHARACTERISTICS  OF  VOLCANOES 

Tyi'KS  ok  Voi.caxoks:  Stromboli;  Vesuviiis;  Krakatoa;  Hawaiian 
islands;  fissure  eruptions;  Deccau  trap;  Coluuihia  lava;  trap 
r  .;ks  of  the  Newark  system \-\o 

Stacks  ix  thk  Livks  ok  Volcanoes j.')-ls 

C'liAHACTKuisTics  OK  THK  PRODUCTS  OK  VoF.cAxoKs :  Gaseous  and 
sublimed  products  ;  lii[uid  and  solid  products;  lava  streams  ;  tun- 
nels in  lava;  aa;  pahoehoe;  scoriaceous  surfaces  of  lava  streams; 
characteristics  of  the  bottoms  of  lava  streams  ;  crystalline  struct- 
ure of  the  central  portions  of  lava  sheets ;  frag-mental  products ; 
driblet  cones ;  Pele's  hair;  bond)s;  scoria  cones;  sheets  of  volcanic 
sand  and  dust 48-80 

Pkokilks  of  Volcanic  ^Mountains 80-.s:5 

Structcre  of  Volcanic  Moi-ntaixs:  Cones  formed  of  projectiles; 


composite  cones ;  dikes;  volcanic  necks  . 
Erosion  of  Volcanic  Mountains 


8:}-9() 
80-94 


Subterranean  Intrusions:    Dikes;  sheets;  plugs;  laccolites;  sub- 

tuberant  mountains ;  generalizations !»4-l()(} 

Characteristics  of  Igneous  Rocks  :  Classification  of  igneous  rocks 
based  on  physical  characters,  —  on  chemical  characters,  —  on  min- 
eralogical  characters ;  granite ;  basalt ;  rhyolite ;  trachyte ;  ande- 
site ;  summary  ....  106-120 


CHAPTER   IT 

General  Distribution  of  the  Active  and  Recently  Extinct 

Volcanoes  of  North  America 127-133 

ix 


CONTENTS 


CHAPTER  III 

Voi.CAXOEs  OF  Ckntual  Amkiuca:  (leneral  geology;  Panama;  list 

of  Central  American  volcanoes l:J4-l;J!) 

Yorxd    Voi.cANoK.s :    Izaico;   birth  of  a  volcano  in   Laiie   Tlopanp^o; 

a  nameless  volcano  in  Nicaragua ;  Jorullo,  Mexico         .         .      1;J!>-1.')0 

Oi.DKR    VoLcAXOKs:    Consegiiliia ;     Volcan    del    Fuego;    Volcan   de 

Agua 15G-171 


CHAPTER  IV 

Voiaaxoes  of  Mf.xico:  Orizaba;  Popocatepetl;  Ixtaccihuatl ;  Xinan- 
tecall ;  Tuxtla;  Cofre  de  Perote ;  C'olima;  volcanoes  of  northern 
Mexico;  volcanoes  of  Lower  California 172-190 


CHAPTER  V 

VoLCAXOKS  OF  THE  United  States  :  San  Francisco  Mountain,  Ari- 
zona; Mt.  Taylor,  New  Mexico;  Ice  Spring  craters,  Utah;  Taber- 
nacle crater,  Utah ;  craters  near  Kagtown,  Nevada ;  Mono  valley, 
California;  Mono  craters;  Mt.  Shasta,  California;  Cinder  cone, 
near  Lassen's  Peak,  California ;  Crater  Lake,  Oregon     .        .      191-233 

The  Great  Volcaxic  Moi  xtaixs  of  Ouegon  and  Washington; 
Mt.  Pitt ;  Three  Sisters  and  Mt.  Jefferson ;  Mt.  Hood  ;  Mt.  Adams ; 
Mt.  St.  Helen's;  Mt.  Rainier  (Tacoraa);  Mt.  Baker       .        .     233-246 

Cascade  Mountains 24G-2.50 

CoLUMhiA  Lava 250-257 

Volcanoes  of  the  Coast  Raxoe 257 

VoLCAxoEs  of   the   Rocky   MOUNTAIN  Regiox  ;   Blackfoot  basin, 

Idaho ;  Colorado ;  Spanish  peaks  ;  New  Mexico ;  Canada       .      257-267 

Volcanoes  of  Alaska:  The  Aleutian  volcanic  belt;  Cook's  Inlet; 
Redoute ;  St.  Augustine ;  Unimak  Island  ;  Bogosloff  Island ;  Una- 
laska  Island ;  central  and  western  Aleutian  islands;  summary,    267-283 


CHAPTER  VI 

Deposits  of  Volcanic  Dust  :  Distribution ;  physical  and  chemical  proper- 
ties ;  economic  importance        .......      284—296 


CONTKNTS 


XI 


CIIAITKK    VII 

TiiEOKKTiCAL  CoNsiDFRATioxs  :  Interior  lifiat  of  the  earth  ;  physical 
conditions  of  the  earth's  interior;  intrnsivo  rocks;  relation  itetween 
intrnsive  rocks  and  volcanoes;  source  of  the  steam  of  volcanoes; 
source  of  the  heat  of  volcanoes;  source  of  the  pressure  which 
causes  nioUen  lava  to  rise  in  fissures  in  the  earth's  crust ;  differ- 
ences in  lavas ;  independence  of  neighboring  volcanoes  ;  origin  of 
fractures  in  the  earth's  crust;  association  of  volcanoes  with  the 
sea ;  influence  of  water  on  volca -ic  eruptions  .        .        .        .     'J07-:U!) 

Otiikr  IIyi'otiiksks:   Chemical  hypothesis;   mechanical  hypothesis; 

steum  hypotheses ;31!>-:L'4 


CIIAITKU   VIII 

LiKK    IIlSTOKY   OF    A    Voj.CANO 


.    ;j27-;i;{.s 


iXDKX 


;):{!) 


fmmvp^mm; 


I    i 


I 


r 


ILLUSTRATIONS 


I'LATK 
1. 


<'t,  Alaska,  1895  I 


8. 
!t. 

10. 

11. 
l-J. 

i;i. 

14. 

V). 

HI 


PLATES 

KAfE    PAliK 

Sketcli  map  of  the  world,  sliowinj,'  distrilmtion  of  volcanoes,  Fmnthpkcn 

A'esiiviiis  ill  (■ruptioii,  1872 g 

*/.    l-'iisiyaiiia,  .Japan 

/'.    St.  An>,Mistine,  Cook's  Inl< 

Skf'tch  ihap  of  North  America,  showing  distrihution  of  volcanoes,     128 

Izalco,  San  Salvador,  1804        .... 

(I.   San  Franci.sco  Monntain,  Arizona  | 

h.    Volcanic  neck  near  Mt.  Taylor,  New  Mexico  S 

Ice  Spring  craters,  Utah  . 

Map  of  ^lono  craters,  California 

Mt.  Shasta,  California 

n.   General  view  of  Cinder  cono,  near  Lassen' 

h.    Section  of  Cinder  cone 

Geological  map  of  Cinder  cone  region,  California  . 

<t.   ;Mt.  Hood,  Oregon    ) 

h.    Crater  of  IVIt.  Hood  S 

n.   Mt.  St.  Helen's,  Washington  ) 

h.    Mt.  Rainier,  Washington        i 

Mt.  Rainier,  Washington 

(t.   Pavloff  volcano,  Alaska  1 

b.  Shishaldin  volcano,  Alaska  S 
a.  Bogosloff  Island,  IJering  Sea  j 
ft.   New  Bogosloff  |^    •        •        •        . 


s  Peak,  California  ) 


,M> 


14l> 
lf»4 

2(10 
•-'16 
224 

228 

2;i0 
2:50 

2:58 

244 

270 

280 


xiii 


XIV 


ILLUSTltATION'a 


riGLKKS 

1.  Stroiiiboli 

2.  Profiles  of  volciiiiie  iiiountuiii.>  .... 

:{.  Kxpuriment  illiiMtrutiuy  the  Mtructiire  of  a  cinder  cone 

4.  Itleal  section  tlirougii  Vesnvius        .... 

f).  DiiiB  on  tiie  shore  of  Lake  Superior 

0.  Si<etcli  of  Conseguina,  Nicaragua     .... 

7.  Map  of  a  part  of  Paoha  Ishiml,  Mono  Lake,  California 

8.  Panuni  crater,  Mono  valley,  California    . 

{».  Sections  of  .small  craters,  Mono  valley,  California  . 

10.  Summit  of  Cinder  cone,  near  Lassen's  Peak,  California 

n.  Volcanic  dust  as  seen  under  the  microscope    . 


1 

si 

M.j 

87 

!)8 

l.-)8 

l.'i:{ 

'Jiiii 

22;» 

2:51 
21)0 


pii^ 


VOLCANOES  OF  NOUTII  AMEltICA 


CIIAPTER   I 


CIIAIIACTKIUSTICS   OF   VOLCAXOKS 


Both  the  historical  and  scientific  interest  in  volcanoes 
originated  in  sontliern  Europe.  Etna,  Vesuvius,  Santorin, 
and  tlie  volcanoes  of  the  Lipari  islands^  figure  in  Greek 
and  llonian  mythology,  and  have  made  a  deep  impression 
on  tlie  history  and  poetry  of  the  Mediterranean  region. 
These  same  volcanoes,  in  later  times,  lead  to  a  scientific 
study  of  the  phenomena  attending  volcanic  eruptions. 
Althougli  the  same  phenomena  that  attracted  the  atten- 
tion of  pliilosophers  to  tlie  volcanoes  of  southern  Europe 
have  heen  manifested  at  hundreds  of  other  localities,  and 
many  times  on  a  far  grander  scale  than  even  Pompeii  has 
witnessed,  yet  on  account  of  the  length  of  time  that 
observations  have  been  carried  on  in  the  region  referred 
to,  and  the  painstaking  accuracy  of  much  of  the  W(jrk 
done  there,  it  will  long  remain  classic  ground  to  the 
student  of  nature,  as  well  as  to  the  historian,  the  poet, 
and  the  painter. 

Types  ob^  Volcanoes 

In  beginning  the  study  of  the  volcanoes  of  North 
America,  it  is  essential  that  we  should  learn  at  least 
the  principal  results  attained  in  other  regions  respecting 


VOLCANOKS   OV    NOIl'l  ir    AMKIMCA 


I    "     ; 


L'^ 


the  cliiinictoi'isticM  of  volcairu!  ('niptloiiH.  For  tills  reason 
as  niiioli  Sparc  as  is  practicable  uinlcr  tin;  plan  I  have 
outliiicd,  will  \)v.  devoted  ;it  tlie  he;j;iimiii;j,'  to  the  con- 
sideration of  tli((  volcanoes  of  sonthern  Knrope.  Some 
attention  will  also  he  <j,iven  to  the  volcanoes  of  Iceland, 
the  Hawaiian  islands,  Japan,  and  the  .lava-Snniatra  region. 

Stromboli.  —  Uisinjj,'  from  the  Mediterranean,  ahout  six- 
teen miles  northwest  of  the  Strait  of  Messina,  is  a  vol- 
canic island  known  as  Stromholi,  on(!  of  the  Li[)ari 
grou]).  Its  general  form  is  that  of  an  irregular  four-sided 
pyramid.  From  an  opening  near  its  sunnnit  steam  es- 
capes almost  constantly,  and  frequently  with  small  explo- 
sions. The  steam  condenses  so  as  to  form  a  peculiar, 
tleecy  cloud  when  illuminated  by  the  sun,  and  glows  at 
night  with  a  ruddy  light  emanating  from  the  highly 
heated  and  frequently  molten  rock  within  the  opening, 
near  the  apex  of  the  island.  Owing  to  the  long  con- 
tinued activity  of  the  volcano,  the  light  reflected  at  night 
from  the  cloud  above  its  sunnnit  .serves  as  a  beacon 
to  mariners,  and  has  made  it  known  as  the  Light-house 
of  the  Mediterranean. 

The  island  of  Stromboli  is  the  expo-^ed  portion  of  a 
large  volcanic  pile,  the  base  of  which  is  deeply  sul)- 
merged.  Its  sunnnit  rises  about  .^000  feet  above 
the  sea,  and  soundings  near  at  hand  show  that  its  base 
is  submerged  to  about  the  same  amount.  Were  the 
sea  removed,  it  would  stand  as  a  pnwipitous,  isolated 
mountain,  rising  from  a  plane  to  a  height  of  GOOO  feet, 
and  with  a  base  five  or  six  miles  in  diameter.  This 
mass  of  material  has  been  forced  out  in  a  molten  or  plas- 
tic condition  from  an  opening  in  the  floor  of  the  sea.  and 
piled  up  about  the  vent.     The  tube  or  conduit,  through 


)& 


.^.^ — *-,^..,^^.j 


-atr.'j.irr  n.'Bttig 


«'H  \U ArTKIMSTfrM   OV    VOM'ANOKH 


of  a 
Hub- 

il)Ove 

base 

the 

lated 

fnet, 

This 

plas- 

and 


wliich  tlic  iiioltcii  nx'k  ascciidcil,  has  been  pndonp'd  by 
tli(>  acciiiiiulatioii  of  tlic  hardened  lava  about  tlic  ori)j,'inal 
(»|»(']dii,u',  and  now  leads  to  near  tlie  siinimit  of  the  island. 
The  eon(hiit  is  still  lilled  with  niobcn  lava  derived  from 
an  unUnown  source,  |>rol»ably  thousands  of  feet  beneath 
(he  llooi'  of  the  iMediturraiiean,  and  from  time  to  lime 
oveillows,  or  exi)losions  blow  out  fra;j,'ments  of  plastic! 
rock,  and  additions  of  fresh  material  are  made  t(<  Hie 
pile.  The  position  of  the  ()penin<^,  through  which  molten 
rock,  accompanied  ))y  great  volumes  of  sieam.  escapes,  is 
chan^u'ed  from  time  to  tinu!,  although  historical  records 
that  such  is  the  case  appear  to  be  indelinite,  and  is  now 
on  the  northwest  side  of  the  mountain,  about  one  thou- 
sand feet  bi'low  the  summit.  This  opening  is  a  cup-shaped 
depre.ssion.  or  crater.  From  it  a  Hat  slope,  Itoundetl  on 
each  side  )»y  steep  cliffs,  and  known  as  the  Sciarra,  de- 
scends at  an  angle  of  al)ont  35°  to  the  sea.  This  steep 
slope,  however,  is  a  peculiar  feature  of  Strondndi,  and 
not  cliaracteristic  of  volcanoes  in  general. 

The  study  of  v(d(!anoes  has  shown  that  they  may,  for 
convenience,  be  divided  into  two  ela.sses — the  t'xplo.sirc  and 
the  fjaid  —  with  reference  to  the  violence  (d"  their  erup- 
tions. Strond)oli  is  an  exampU;  of  the  former  class,  but  is 
usually  in  a  nuld  state  of  activity,  and  thus  favoral)le  for 
observing  the  characteristics  of  volcanic  eruptions. 

The  nature  of  the  eruptions  usually  in  progress  at 
Stroud)oli  has  been  graphically  described  ))y  Judd,^  who 
visited  the  island  in  April,  1874,  as  follows : 

*  J.  W.  Jiuld.  "Volcanoes,"  luternntiondl  Srienti/ic  .S^r/V.f.  Apjileton  Ik 
Co.,  ISSI,  This  book  is  recommended  to  students.  From  it  much  of  the 
information  presented  in  tlie  present  volume  concerning  the  characteristics 
of  volcanoes  lias  been  either  directly  or  indirectly  obtained. 


I  I 


hi 


'    i  I 


4  VOLCANOES  OF   NORTH    AMEUICA 

'"  Oil  reaching  n  point  upon  the  side  of  the  Sciarra, 
from  wliieii  tlie  crater  was  in  full  view  before  me,  I  wit- 
nessed and  made  a  sketch  of  an  outbrealv  which  took 
place.  [Tiiis  sketch  is  reproduced  in  Fig.  1.]  Before  the 
outburst,  numerous  light  curling  wreaths  of  vapor  were 
seen  ascendimr  from  fissures  on  the  sides  and  bottom  of 
the  crnter.  Suddenly,  and  without  the  slightest  warning, 
a  sound  was  hearci  like  that  produced  when  a  locomotive 
blows  off  its  steam ;  a  great  volume  of  watery  vapor  was 


Fig.  1.    The  crater  of  Stromboli  as  viewed  from  the  side  of  the  Seiarra  during  an 
eruption  on  the  morning  of  April  24,  1874.    (After  J.  W.  Judd.) 

at  the  same  time  thrown  violently  into  the  atmosphere, 
and  with  i^  there  were  hurled  upwards  a  number  of  dark 
fragments,  which  rose  to  a  height  of  400  or  500  feet 
above  tlie  crater,  describing  curves  in  their  course,  and 
then  falling  l)ack  upon  the  mountain.  Most  of  the  frag- 
ments tumbled  into  the  crater  with  a  loud,  rattling  noise, 
but  some  of  them  fell  outside  the  crater,  and  a  fev/  rolled 
down  the  steep  slope  of  the  Sciarra  into  the  sea.  Some 
of  these  fallim»:  fragments  were  found  to  be  still  hot  and 
glowing,  and  in  a  semi-molten  condition,  so  that  they 


j 


V! 


CIIARACTEllISTICS   OF    VOLCAXOES 


readily  received  the  impression  of  a  coin  thrust  into 
tlieni." 

From  ahove  the  crater,  wlien  the  direction  of  the  wind 
is  favorable,  one  can  look  down  into  the  fiery  caldroii  and 
learn  more  of  the  nature  of  the  eruptions  that  take  place. 
From  such  a  point  of  view,  as  described  by  Judd,  '•  The 
black,  slaggy  ]x)ttom  of  the  crater  is  seen  to  be  traversed 
by  many  Assures  or  cracks,  from  most  of  which  curhng 
jets  of  vapor  issue  quietly,  and  gradually  mingle  with  and 
disappear  in  the  atmosphere.  But  besides  these  smaller 
cracks  at  the  bottom  of  the  crater,  several  larger  openings 
are  seen,  Avhich  vary  in  number  and  position  at  different 
periods  ;  sometimes  only  one  of  these  apertures  is  visible, 
at  other  times  as  many  as  six  or  seven,  and  the  phenomena 
presented  at  these  larger  apertures  are  especially  worthy 
of  careful  investigation. 

"  These  larger  openings,  if  we  study  the  nature  of  the 
action  taking  place  at  them,  may  be  divided  into  three 
classes.  From  those  of  the  first  class,  steam  is  emitted 
with  loud,  snorting  puffs,  like  those  produced  by  a  loco- 
motive engine,  but  far  less  regular  and  rhythmical  in 
their  succession.  In  the  second  class  of  apertui'es  masses 
of  molten  material  are  seen  welling  out,  and,  if  the 
position  of  the  aperture  be  favorable,  flowing  outside 
the  crater ;  from  this  liquid  molten  mass  steam  is  seen  to 
escape,  sometimes  in  considerable  quantities.  The  open- 
ings of  the  third  class  present  still  more  interesting  ap- 
pearances. Within  the  walls  of  the  apertures  a  viscid 
or  semi-liquid  substance  is  seen  slowly  heaving  up  and 
down.  As  we  watch  the  seething  mass,  the  agitation 
within  is  observed  to  increase  gradually,  and  at  last  a 
gigantic  bubble  is  formed  which  violently  bursts,  when 


6 


VOLCANOES   OF    NOIITH    AMKUICA 


a  great  rush  of  steam  takes  place,  carrying  fragments 
of  the  scum-like  surface  of  the  liquid  high  into  the 
atmosphere. 

"  If  we  visit  the  crater  by  night,  the  appearances  pre- 
sented are  found  to  be  still  more  striking  and  suggestive. 
The  smaller  cracks  and  larger  openings  glow  with  a  ruddy 
light.  The  liquid  matter  is  seen  to  be  red-hot  or  even 
white-hot,  while  the  scum  or  crust  which  forms  upon  it  is 
of  a  dull  red  color.  Every  time  a  bubble  bursts  and  the 
crust  is  broken  up  by  the  escape  of  steam,  a  fresh,  glowing 
surface  of  the  incandescent  material  is  exposed.  If  at 
these  moments  we  look  up  at  the  vapor  cloud  covering 
the  mountain,  we  shall  at  once  understand  the  cause  of 
the  singular  appearances  presented  by  Stromboli  when 
viewed  from  a  distance  at  ni^^ht,  for  the  great  masses  of 
vapor  are  seen  to  be  lit  up  with  a  vivid,  ruddy  glow,  like 
that  produced  when  an  engine  driver  opens  the  door  of 
the  furnace  and  illuminates  the  stream  of  vapor  issuing 
from  the  funnel  of  his  locomotive." 

The  bursting  of  great  bubbles  of  steam  on  the  surface 
of  the  viscid  lava  within  the  crater  accounts  for  the 
globular,  fleece-like  masses  of  vapor  that  give  a  special 
feature  to  the  steam  cloud  seen  above  Stromboli.  Similar 
concentric  masses  of  vapor  are  a  characteristic  portion 
of  the  vapor  columns  that  rise  from  many  volcanoes 
during  calm  weather.  An  essential  element,  at  least  of 
the  less  violent  eruptions  of  volcanoes,  is  thus  .shown  to 
be  the  breaking  of  huge  bubbles  of  steam. 

The  fact  of  special  significance  to  be  noted  in  the  account 
of  a  mildly  explosive  volcanic  eruption  just  cited,  is  that 
the  throat  of  the  volcano  is  filled  with  molten  rock,  por- 
tions of  which  are  violently  ejected  from  time  to  time  by 


n 


CHARACTERISTICS    OF    VOLCANOES 


the  e?cape  of  steam  which  rises  through  the  liquid  lava. 
These  fragments  of  semi-m(jlten  rock  are  hurled  into  the 
air  and  fall  in  part  about  the  opening  from  which  they 
were  ejected,  and  build  up  a  rim  about  it.  A  conical 
pile  of  this  nature  with  an  opening  in  its  summit,  is 
termed  a  cinder  cone.  We  also  note  that  sometimes  the 
molten  rock  overflows  the  crater  and  descends  the  moun- 
tain as  a  lava  stream.  These  features,  as  will  be  seen 
later,  are  characteristic  of  the  eruptions  of  many  volcanoes. 

Althci^gh  Stromboli  is  usually  in  a  state  of  mild  ac- 
tivity, yet  occasionally  the  violence  of  its  explosions  is 
greatly  increased.  The  roar  of  the  escaping  steam  may 
then  be  heard  for  many  miles ;  fragments  of  plastic  rock 
are  hurled  thousands  of  feet  into  the  atmosphere,  and 
scattered  not  only  over  the  entire  island,  but  fall  in  the 
surrounding  waters ;  and  streams  of  molten  rock  flow 
down  from  the  crater  into  the  sea. 

Vesuvius.  —  This  world-famed  volcano,  situated  near 
the  shore  of  the  Bay  of  Naples  and  about  ten  miles  east- 
ward of  the  city  of  Naples,  is  a  charming  and  most  beauti- 
ful object  wdien  beheld  from  afar.  The  first  evidence  of 
its  presence  that  usually  meets  the  gaze  of  the  expectant 
traveller,  whether  approaching  over  the  blue  sea  or  through 
the  picturesque  land,  is  a  vast  column  of  steam,  rising 
tranquilly  far  above  the  mountain's  summit,  and  then 
expanding  into  a  broad,  vapory  canopy.  When  the  wind 
is  not  too  strong,  the  cloud  is  seen  to  be  made  up  of 
concentric,  fleecy  masses,  each  one  of  which,  as  in  the 
case  of  the  cloud  above  Stromboli,  is  due  to  the  explosion 
of  a  great  steam  bubble  in  the  caldron  of  molten  rock 
from  which  it  rose.  The  vertical  shaft  of  steam  with  its 
expanded  summit  resembles  in  general  form  the  outlines 


8 


VOLCANOES   OF   NORTH   AMEllICA 


of  the  characteristic  stone  pine  of  Italy,  and  for  this  reason 
is  widely  known  as  the  ^^me  tree  of  Vesuvius. 

Vesuvius  is  a  conical  mountain  about  4000  feet  high. 
From  the  Bay  of  Naples  the  steep  conical  summit  is  seen 
to  rise  within  the  truncated  and  half-destroyed  crater  of 
an  older  and  much  larger  volcano,  the  highest  portion  of 
which  has  an  elevation  cf  3730  feet.  The  portion  of  the 
rim  of  the  older  crater  still  remaining  is  termed  Mt. 
Somma. 

Previous  to  the  Christian  era,  Vesuvius  was  familiar 
to  the  Romans  as  a  conical  mountain  with  a  truncated 
summit,  in  which  there  was  a  deep  depression  some  three 
miles  in  diameter.  From  the  earliest  historic  times  to  the 
year  79,  the  volcano  was  dormant  and  its  crater  cold  and 
overgrown  with  vegetation.  In  the  year  mentioned,  an 
explosion  of  remarkable  violence  occurred,  which  blew 
away  a  large  portion  of  the  ancient  crater  and  buried 
Pompeii  and  Herculaneum  beneath  the  fragmental  prod- 
ucts that  were  ejected.  It  was  during  this  eruption  that 
Pliny  lost  his  life,  while  iTxaking  observations  on  the 
earliest  volcanic  explosion  of  which  history  retains  a 
definite  record.^  A  portion  of  the  wall  of  the  ancient 
crater,  referred  to  above  as  Mt.  Somma,  was  left,  and 
within  its  embrace  the  modern  Vesuvius  has  been  built. 

The  volcano,  which  gives  a  matchless  charm  to  a 
thousand  picturesque  vistas  in  the  vicinity  of  Naples, 
has,  like  Stromboli,  its  periods  of  mild  activity,  inter- 
rupted at  irregular  intervals  by  explosive  eruptions  of 
great  violence,  which,  in  many  instances,  are  accompanied 

^  This  tragic  event  was  minutely  and  graphically  recorded  by  Gains 
Plinius,  the  younger  Pliny.  A  translation  of  this  account  may  be  found  in 
Shaler's  "  Aspects  of  the  Earth."    New  York,  1889,  pp.  50-56. 


irti 


^^  ■-:^.-:^-.^:l  '■■,-  ....J>..-      .  f^- 


SJWjWfffife'.  ^- 


VOLCANOES   OF  NC^RTII   AMKRK'A. 


PLATK  '.». 


Fic.  A.     Vesuvius  in  eruption.     As  seen  from  Naples.  .'?  p.m.,  April  '2(!,  1S72. 


Fig.  B.    Vesuvius  in  eruption.     As  seen  from  Naples,  3.?'J  p.m.,  April  2«,  1872. 


mi 


CHARACTEIUSTICS   OF    VOLCANOES 


9 


hy  overflows  of  lava.  Unlike  Stromlmli,  however,  the 
variations  in  its  activity  are  strongly  prononnced.  At 
times  Vesuvius  is  dormant  for  many  years  and  even  for 
centuries,  and  again  awalens  to  an  activity  of  such 
energy  that  southern  Italy  is  shaken  hy  eartlK|uakos, 
steam  escapes  in  explosions  so  violent  as  to  hurl  stone 
and  dust  high  m  the  air,  and  even  hlow  away  and  dis- 
trihute  far  and  wide  over  the  adjacent  region  the  material 
previously  forming  the  summit  of  the  mountain.  While 
Stromboli  since  the  dawn  of  history  has  been  in  a  state  of 
mild  activity,  interrupted  at  long  intervals  by  explosions 
of  greater  violence,  Vesuvius  has  been  alternately  dormant 
and  its  summit  cold,  and  again  an  object  of  dread  which 
has  brought  destruction  and  death  to  the  fair  land  sur- 
rounding it.  These  two  volcanoes  belong  to  the  explosive 
type,  as  the  student  will  appreciate  more  fully  in  advance, 
but  illustrate  two  quite  well  marked  phases  of  that  type, 
which  have  been  recognized  also  in  many  other  volcanoes, 
and  are  termed  the  Stromholian  stage  and  the  Vesuvian 
stage,  —  the  former  characterized  by  long-continued  but 
mild  activity,  the  second  by  periods  of  rest  bvoken  by 
explosions  of  extreme  violence. 

When  Vesuvius  is  in  a  mild  state  of  activity,  approach- 
ing that  normal  to  Stromboli,  one  may  safely  climb  to  the 
edge  of  the  great  bowl  which  usually  exists  at  the  summit 
and  even  descend  into  it,  and  observe  the  nature  of  the 
molten  rock  that  rises  from  below,  the  manner  in  which 
the  steam  escapes  from  its  enclosing  magma,  etc. 

In  November,  1879,  I  climbed  the  cone  composed  of 
loose  fragments  of  lava,  forming  the  summit  portion  of 
Vesuvius,  and  reached  the  rim  of  the  bowl-shaped  depres- 
sion at  the  summit.     The  crater  near  the  summit  then 


1 1 


10 


VOLCANOKS   OF    NOKTIf    AMKItICA 


! 

t 

I 


had  an  outer  slope  of  al)oiit  35° ;  tlie  inner  slope  was  more 
precipitous,  Jind  exposed  the  edges  of  out\vard-dij)[)ing 
layers  of  fragmental  material,  showing  that  the  opening 
had  not  long  previously  been  enlarged  by  tiie  l)lowing 
away  of  the  iuner  portion  of  its  rim.  This  occurred 
periiaps  during  the  energetic  eruption  of  1872.  Tlie 
crater  was  by  eye  measurement  150  to  200  feet  deep,  and 
a  thousand  feet  in  diameter.  It  was  floored  with  black, 
slag-like  lava.  The  lava  in  many  places  was  wrinkled  or 
corrugated,  owing  to  slow  movement  before  cooling,  and 
intersected  by  numerous  fissures  through  which  the  glow- 
ing, red-hot  rocks  beneath  could  be  plainly  seen.  From 
some  of  the  fissures,  steam  was  escaping  with  a  hissing 
noise.  In  the  central  portion  of  the  floor  of  hardened 
lava,  and  resting  on  it,  was  a  rough,  conical  pile  of  slag- 
like lava,  rising  to  a  height  nearly  as  great  as  the  highest 
point  on  the  encircling  rim.  This  inner  pile  was  the 
cone  of  eruption.  From  its  summit  great  volumes  of 
vapor  were  rolling  out,  accompanied  by  puffs  which  sent 
globular  masses  of  steam  high  in  the  air.  With  each 
puff,  stones  four  or  five  inches  in  diameter  and  highly 
heated,  were  hurled  to  a  height  of  between  one  and  two 
hundred  feet  in  the  air.  Some  of  the  stones  fell  on  the 
sides  of  the  conical  pile,  and  occasionally  one  would  roll 
to  its  base.  At  each  explosion  the  entire  crater  vibrated, 
but  not  sufficiently  to  be  at  all  alarming.  I  descended  to 
the  floor  of  the  crater,  and  could  walk  with  safety  over 
the  recently  congealed  lava,  although  it  was  hot  to  the 
feet.  One  could  easily  thrust  a  walking-stick  through 
the  crevices  and  into  the  still  semi-molten  lava  beneath. 
On  gaining  the  base  of  the  cone  of  eruption,  I  clambered 
about  half-way  up  its  rough  sides,  but,  as  the  wind  was 


m 


■-i- 


CIIAUACTKRISTICa   OK    VOLCANOES 


11 


not  strong  or  regular  in  any  ono  dirootion,  tlio  stonos 
liurltMl  into  the  air  at  each  explosion  fell  all  about  the 
central  orifice,  while  the  steam  and  gases  hecanie  more 
and  more  dense  near  the  sununit.  The  pulsating  and 
rumbling  of  the  molten  material  within  the  crater  could 
be  distinctly  heard,  and  the  trembling  of  the  rocks  at 
each  explosion  when  a  belch  of  steam  (jccurred,  made  it 
troublesome  to  stand  erect.  Although  prevented  from 
seeing  the  actual  boiling  of  the  lava  within  the  crater, 
this  omission  can  be  supplied  by  observations  made  by 
N.  S.  Shaler,^  i)i  the  winter  of  1882  : 

"  Taking  advantage  of  a  strong  gale  from  the  north, 
the  well-known  tramontana  of  Italy,  it  was  possible  to 
creep  up  to  the  very  edge  of  the  crater  and  look  down 
upon  the  surface  of  the  boiling  lava,  from  which  the 
gases  were  breaking  forth.  Although  the  pit  was  Tiom 
time  to  time  filled  with  whirling  vapor,  the  favoring  wind 
often  swept  it  away  so  that  for  a  few  seconds  it  was 
possible  to  see  every  feature  of  the  terrifying  scene. 
Several  times  a  minute  the  surface  of  the  tossed  lava  was 
rent  by  a  violent  explosion  of  gases,  which  appeared  to 
hurl  the  whole  mass  of  fluid  rock  into  the  air.  The 
ascending  column  of  vapor  and  lava  fragments  rose  as 
a  shaft  to  a  height  of  several  hundred  feet.  Many  of 
the  masses,  which  seemed  to  rise  with  the  ease  of  bubbles, 
were  some  feet  in  diameter,  and  made  a  great  din  as  they 
crushed  down  upon  the  surface  on  the  southward  side  of 
the  crater.  They  often  could  be  seen  to  fly  into  frag- 
ments as  they  ascended.  At  the  moment  of  the  explosion 
the  escaping  gases  appeared  transparent,  a  few  score  feet 
above  the  point  of  escape  the  ejected  column  became  of  a 

1  "  Aspects  of  the  Earth."     New  York,  1889.    pp.  62-64. 


/^' 


12 


VOLCANOES   OK    NOUTir    AMKUICA 


il; 


V 


-I  • 

I': 
I' 


stool-gray  color,  and  a  litth;  liigluM'  it  chanjjiod  to  tlio 
(!liaractoi'isti(3  Imo  of  stoain.  That  it  was  steam  sli<^litly 
mixed  with  other  j^asos  was  evidcMit  whenever  in  its 
whirling  movements  the  vaporous  column  swept  around 
t)\G  point  of  ohservation.  The  curious  '•  work-day  odor  " 
of  steam  was  perfectly  ai)parent,  togetlier  with  the 
pungent  sense  of  sidphurous  fumes  suggestive  of  an 
infernal  laundry. 

"  Although  the  heat  at  the  moment  of  explosion  was 
great,  it  was  possible,  with  the  shelter  to  the  face  secured 
by  an  extemporized  mask,  to  avoid  any  serious  conse- 
quences from  it,  and  even  to  make  some  rather  rude  and 
unsatisfactory  diagrams  of  the  scene.  The  principal  ob- 
stacle to  observation  arose  from  the  violence  of  the  shocks 
given  to  the  cone  and  propagated  through  the  air  by  tlie 
explosions,  which  made  it  extremely  difficult  to  fix  the 
attention  on  the  phenomena.   .  .  . 

"As  if  to  complete  the  illustration  of  volcanic  phenom- 
ena which  this  little  outbreak  afforded,  there  was  a  small 
rivulet  of  lava  pouring  from  the  low  wall  of  cinders  on 
one  side  of  the  cone  and  flowing  quietly  down  the  slope. 
It  was  not  much  larger  than  the  stream  of  liquid  iron 
which  flows  from  an  iron-furnace  to  the  moulds  which 
await  it,  but  in  the  motion  all  the  essential  features  of 
the  greatest  of  these  fiery  torrents  could  be  seen.  The 
surface  of  the  fluid,  cooled  in  the  air,  slowly  hardened 
into  a  viscid  scum.  This  scum,  urged  forward  by  the 
swifter  movement  of  the  more  fluid  matter  below,  was 
wrinkled  as  is  the  cream  on  a  pan  of  milk  when  it  is 
slowly  poured  over  the  edge  of  the  vessel." 

Two  of  the  most  important  phases  of  volcanic  eruptions 
are  illustrated   by  the  observations   just  cited ;   one  the 


CIIAUALTKKISTICS    OF    VOLCANOKS 


13 


l)l()wiiig  out  of  rock  fra,L!,iiit'iit.s  by  .stoam  (.'X[)lu.sion.s,  tlu; 
otlicr  tlie  ovL'illow  of  moltuii  rock.  Tlioso  are  the  cliiof 
inaiiil'estatioiis,  with  tlio  uxcuptiou  of  tlio  c.scai)e  of  vast 
volimios  of  steaiii,  tliat  attract  the  attention  in  all  volcanic 
oniptions,  and  may  occur  .separately  or  be  united  in  the 
same  outbreak. 

The  mild  ex[)lo.sions  and  rivulet.s  of  lava  characteristic 
of  the  eruptions  of  Stromboli  and  of  the  more  subdued 
phases  of  Vesuvins  when  in  action,  have  but  to  be  in- 
creased in  intensity  and  vohunc,  to  enable  one  to  ai)pre- 
ciate  the  nature  of  even  the  most  stupendous  volcanic 
outbreak  that  the  world  has  ever  witnessed.  The  proxi- 
mate cause  of  the  ex[dosions  in  the  eruptions  described 
aljove  is  plainly  the  expansive  energy  of  steam.  The  ori- 
gin of  the  steam,  the  cause  of  the  i)ressure  on  the  molten 
rock  which  forces  it  npward,  and  the  source  of  the  heat 
that  licpiefies  the  hiva,  will  be  considered  in  advance. 

Vesuvius,  as  already  stated,  was  dormant  from  its  first 
mention  in  history  until  the  year  79  of  the  Christian  era. 
Its  grandest  eruptions  probably  occurred  in  prehistoric 
times,  since  the  ancient  crater,  of  which  Mt.  Sonmia  is  a 
remnant,  was  of  far  greater  magnitude  than  the  modern 
Vesuvius.  By  restoring  the  curve  of  the  portion  of  the 
ancient  crater  wall  wliich  remains,  it  may  be  shown  that 
the  Somma  crater  was  fully  three  miles  in  diameter,  and 
probably  more  lofty  than  the  summit  of  the  modern  cone 
within  it.  The  duration  of  the  last  prehistoric  period  of 
quiescence  is  unknown,  but  probably  embraced  several 
thousand  years,  since  the  floor  of  the  crater  was  cold  and 
solid,  and  overgrown  with  vegetation,  previous  to  the 
eruption  of  79.  It  was  in  this  natural  fortress  that 
Spartacus  and  his  band  of  gladiators  took  refuge. 


14 


VOU'ANOKS   UK    Nouril    AMKUICA 


I  I 


ifj, 


l( 


!'  I 


Souk;  of  tlio  fcatiiros  of  tli«'  <^ro;vt  eruption  of  7'.)  are 
ruconlt'd  in  tlio  acooiml  i^ivcn  \)y  tiu;  }'oiin<;(!r  Pliny 
iilruady  niforrud  to.  lie  HtJitos  tiiat  Wis  uiH^h!  "  was  at 
iMisenuiii  [on  tlic  west  Hidu  of  tlio  Hay  of  Naplo.s,  about 
twonty  uiiit's  in  a  direct  lino  from  Vesuvius]  and  was  in 
couiniand  of  the  fleet  there.  It  was  at  one  o'elock  in  the 
afternoon  oi  the  24th  of  Au<j;ust  that  my  mother  called 
his  attention  to  a  cloud  of  unusual  ai)|)(!aran(!e  and 
size.  ...  A  cloud  was  risinj^^  from  one  of  the  hills  (it 
was  not  then  clear  which  one,  as  the  observers  were 
lookin<^  from  a  distance,  but  it  proved  to  be  Vesuvius), 
which  took  the  likeness  of  a  stone-pitie  very  nearly.  It 
imitated  the  lofty  trunk  and  the  spreading  branches,  for, 
as  I  supposes  the  smoke  had  been  swept  rapidly  ui)ward 
by  a  recent  breeze  and  was  then  left  hanging  unsupi)orted, 
or  else  it  spread  out  laterally  by  its  own  weight  and  grew 
thinner.  It  changed  color,  sometimes  looking  white,  and 
sometimes,  when  it  carried  up  earth  or  ashes,  dark  and 
streaked."  Leaving  Misenum  in  his  ships,  Pliny  the  elder 
proceeded  toward  the  head  of  the  bay.  "  Ashes  began  to 
fall  on  his  ships,  thicker  and  hotter  as  they  approached 
the  land.  Cinders  and  pumice,  and  also  black  fragments 
of  rock  cracked  by  heat,  fell  around  them.  The  sea 
suddenly  shoaled,  and  the  shores  were  obstructed  by 
masses  from  the  ?) mountain."  An  account  of  the  death 
of  Pliny,  suffocated  by  gases  from  the  volcano,  then 
follows. 

In  another  letter  the  younger  Pliny  describes  his  flight 
with  his  mother  from  Misenum.  "  It  was  now  seven 
o'clock  [on  the  morning  of  August  25],  but  the  light  was 
still  faint  and  doubtful.  The  surrounding  buildings  had 
been  badly  shaken,  and  though  we  were  in  an  open  spot 


1:1, 


<. 


(■HAUAUTKUISTICS   UF    VOLCANolirt 


16 


[a  littl(>  yard  bctwoeu  liis  uiuilo's  hoiiso  and  tlio  soa],  tlio 
.s[)acL'  was  mo  Hiiiall  that  tli(!  daii^^^or  of  a  catastropli'j  from 
falliii"^  walls  wa.s  gruat  and  (HTtain.  Not  till  tlicn  <lid 
wo  make  u[)  our  minds  to  go  from  tlio  town.  .  .  .  When 
wo  woro  froo  from  tlio  buildings  wo  ytoitp-'d.  Tlioro  wo 
saw  many  wondors  and  ondnrod  many  terrors.  Tlio 
voliiclos  wo  had  ordorod  to  bo  Ijroiight  out  k('[)t  miming 
l)aokward  and  forward,  though  on  lovol  ground  ;  and  ovon 
when  scotchod  with  stonos  thoy  would  not  koop  still. 
Bosido.s  this,  wo  saw  tho  soa  sucked  down  and,  as  it  woro, 
drivon  back  hy  tho  oarthquako.  Thoro  can  bo  no  doubt 
that  tho  slun'o  had  advanced  on  tho  sea,  and  many  marine 
animals  wore  loft  high  and  dry.  On  the  other  side  was  a 
dark  and  dreadful  cloud,  which  was  broken  by  zigzag  and 
rai)idly  vibrating  Hashes  of  (ire,  and  yawning  showed 
long  shapes  of  flame.  These  were  like  lightnings,  only 
of  greater  extent.   .  .  . 

"  Pretty  soon  the  cloud  began  to  descend  over  tho 
earth  and  cover  the  sea.  It  enfolded  Capron)  and  hid  also 
the  promontory  of  Misenuni."  The  llight  was  continued. 
"Ashes  now  fell,  yet  still  in  small  amount.  I  looked 
back.  A  thick  mist  was  close  at  our  heels,  which  fol- 
lowed us,  spreading  out  over  the  coimtry,  like  an  in- 
undation." Turning  from  the  road  in  order  to  avoid 
the  fleeing,  terror-stricken  throng,  they  rested.  "  Hardly 
had  we  sat  down  when  night  was  over  us  —  not  such  a 
night  as  when  there  is  no  moon  and  clouds  cover  the  sky, 
but  such  darkness  as  one  finds  in  close-shut  rooms.  One 
heard  the  screams  of  women,  the  fretting  cries  of  babes, 
the  shouts  of  men.   .  .  . 

"Little  by  little  it  grew  light  again.  We  did  not 
think  it  the  light  of  day,  but  a  proof  that  the  fire  was 


T 


•-,     .u 


fmmmam 


mmmm^^mt 


it  i 


t   i 


ill  I 


\%\) 


*' 


I'; 

I 


IP. 


VOLCANOES   OF   NORTH   AMERICA 


coming  nearer 


It  was  indeed  fire,  but  it  stopped  afar 
off ;  and  then  there  was  darkness  again,  and  again  a  rain 
of  ashes,  abundant  and  heavy,  and  again  we  rose  and 
shook  them  off,  else  we  had  been  covered  and  evea 
crushed  by  the  w(ught.  ...  At  last  the  murky  vapor 
rolled  away,  in  disappearing  smoke  or  fog.  Soon  the 
real  daylight  appeared  ;  the  sun  shone  out,  of  a  lurid  hue, 
to  be  sure,  as  in  an  eclipse.  The  whole  world  which  met 
our  frightened  eyes  was  transformed.  It  was  covered 
with  ashes  white  as  snow."  Young  Pliny  and  his  mother 
returned  to  Misenum,  and  survived  the  perils  to  which 
they  were  exposed. 

During  this  eruption  Pompeii  was  buried  beneath  dust 
and  "  ashes,"  and  its  site  obliterated  and  lost  to  memory 
for  many  centuries.  Herculaneum,  situated  still  nearer 
the  mountain,  was  overwhelmed  by  similar  material 
(light,  gray,  pumiceous  lapilli),  mixed  with  water  and 
forming  a  mud  which  has  since   hardened   like  cement. 

In  the  narrative  just  cited,  there  is  no  mention  of  lava 
having  been  seen  flowing  from  the  mountain.  The  eruption 
was  caused  by  a  stupendous  outburst  of  steam,  which  dis- 
integrated the  lava  that  rose  with  it,  and  spread  the  fine 
fragments  far  and  wide  over  southern  Italy.  The  essen- 
tial features  of  this  vast  exhibition  of  the  pent-up  energy 
of  subterranean  steam,  may  be  witnessed  to-day  in  the 
little  explosions  that  characterize  the  Strombolian  stage 
of  numerous  volcanoes. 

Following  the  Plinian  eruption  Vesuvius  became  quiet 
once  more,  but  whether  the  escape  of  steam  completely 
ceased  or  not,  is  not  definitely  known.  The  next  eruption 
of  which  some  account  is  extant,  occurred  in  the  year 
203.     Again  in  472  an  eruption  of  paroxysmal  violence 


CHAIIACTERISTICS   OF    VOLCANOES 


17 


took  place,  wliicli  destroyed  villages  that  had  been  built 
over  the  buried  cities  of  Herculaneum  and  Pompeii^  and 
ejected  lapilli  to  so  great  a  height  that  it  fell  as  far  from 
the  mountain  as  Constantinople.^ 

During  a  period  of  nearly  600  years  following,  only 
three  eruptions  are  recorded.  These  were  in  512,  085, 
and  993.  Simi^a'  paroxysms  of  violent  activity  separated 
by  long  periods  of  quiescence  and  of  even  total  cessation 
of  energy,  have  marked  the  behavior  of  Vesuvius  to  the 
present  time.  A  summary  of  what  is  known  concerning 
the  changes  the  mountain  has  experienced  during  this 
lonpj  period  may  be  found  in  Lobley's  work  just  cited. 

The  importance  of  a  knowledge  of  the  behavior  of 
Vesuvius  to  the  inhabitants  of  the  rich  and  populous 
region  surrounding  it,  came  at  length  to  be  fully  appre- 
ciated. About  thirty  years  since,  an  observatory  was 
established  on  a  western  spur  of  the  mountain,  for  the 
purpose  of  keeping  a  record  of  the  behavior  of  the  vol- 
cano, as  well  as  of  meteorological  phenomena  and  earth- 
quake disturbances.  The  Observatory  since  its  opening 
has  been  in  charge  of  Professor  Luigi  Palmieri,  a  well- 
known  physicist  of  long  experience.  A  special  feature 
in  the  equipment  of  the  Observatory  is  furnished  by  the 
instruments  known  as  seismographs,  for  recording  vibra- 
tions of  the  earth. 

To  Palmieri' s  skill  as  an  observer,  and  the  records 
of  the  instruments  of  the  Observatory,  and  also  to 
the  application  of  photography  in  recording  volcanic 
phenomena   (Plate  2),  we  are  indebted  for  the  detailed 


1  J.  L.  Lobley,  "Mount  Vesuvius,"  London,  1889,  pp.  101,  102.  This 
book  contains  the  most  instructive  description  and  historj"^  of  Vesuvius 
accessible  to  the  student. 


18 


VOLCANOES   OP  NOUTH   AMERICA 


n 


if 


'7 


t 


history  of  the  remarkable  outbreak  of  Vesuvius  in  1872.* 
A  marked  feature  of  this  eruption  was  the  pouring  out  of 
streams  of  molten  rock  or  lava. 

After  being  in  a  quiescent  state  from  November,  1848, 
Vesuvius  commenced  to  show  signs  of  renewed  activity  in 
1871,  which  continued,  with  moderate  lava  flows,  for 
several  months.  Early  in  1872,  lava  was  poured  out, 
some  of  the  streams  running  for  a  week  at  a  time.  Fol- 
lowing these  more  quiet  discharges  came  a  violent  ex- 
plosive eruption  accompanied  by  voluminous  lava  streams, 
which  culminated  on  April  26.  The  following  account  of 
this  eruption  has  been  compiled  from  Palmieri's  report 
cited  above : 

On  April  23  the  Observatory  instruments  were  agitated, 
the  activity  of  the  crater  increased,  and  on  the  evening 
of  the  24th  lava  streams  descended  the  cone  in  various 
directions.  All  of  these  lava  streams  were  nearly  ex- 
hausted on  the  morning  of  the  25tli ;  only  one  remaining, 
which  issued  from  the  base  of  the  cone,  not  far  from  the 
spot  where  a  similar  stream  had  issued  during  the  pre- 
ceding montli.  During  the  succeeding  night  a  party  of 
students  visited  the  scene  of  the  disturbance.  A  cloud  of 
smoke  accompanied  by  a  hail  of  hot  projectiles  envelope (1 
them  when  they  were  close  to  the  lava  torrent,  and  ei^'hi 
of  the  party  are  known  to  have  perished. 

A  fissure  opened  on  the  northwest  side  of  the  cone  and 
extended  into  the  depression  known  as  Atria  del  Cavallo, 
which  separates  the  modern  cone  of  Vesuvius  from  the 
fragment  of  an  ancient  crater  rim,  named  Mt.  Somma. 
The  length  of   this  fissure  was  about  1800  feet.     Lava 

1  "  The  Eruption  of  Vesuvius  in  1872,"  by  Professor  Luigi  Palmieri,  -wii'i 
notes.     Edited  by  Robert  Mallet.     London,  1873.    pp.  81-102. 


CHARACTERISTICS   OF   VOLCANOES 


lU 


was  poured  out  from  its  lower  part,  which  extended  into 
tlie  Atria.  Another  fissure  opened  in  the  soutli  side  of 
the  cone,  but  did  not  extend  to  its  base,  and  also  emitted 
a  stream  of  lava.  Streams  of  lava  of  less  importance 
furrowed  the  cone  in  other  directions,  but  the  laru-est 
quantity  came  from  the  fissure  first  mentioned;  the  one 
in  Atria  del  Cavallo.  This  lava  stream  was  for  some 
time  restrained  in  the  Atria,  in  holes  and  inerpialities  of 
a  lava  flow  of  the  previous  years,  but  these  being  filled,  it 
divided  into  two  branches  ;  the  smaller  branch  flowing 
toward  Resina,  near  the  site  of  buried  Ilerculaneum, 
about  five  miles  from  Naples ;  the  larger  branch  took  a 
more  westerly  course,  and  precipitated  itself  into  a  valley, 
known  as  Fossa  della  Vetrana,  occupied  its  whole  width, 
about  2400  feet,  having  advanced  nearly  4000  feet  in 
three  hours.  This  larger  branch  of  the  original  stream 
again  divided,  and  one  branch  partially  overwhelmed  the 
villages  of  Massa  and  St.  Sebastiano,  situated  southwest 
of  Vesuvius  and  about  three  and  a  half  miles  from  its 
summit. 

On  the  night  of  the  26th,  the  Observatory  lay  between 
two  streams  of  molten  lava,  which  emitted  such  an  in- 
tense heat  that  the  glass  in  the  windows  cracked  and  the 
smell  of  scorching  was  perceptible  in  the  rooms. 

The  cone,  besides  being  furrowed  b}-  the  lava  streams 
just  described,  was  traversed  by  several  others  of  smaller 
size  and  briefer  duration.  In  fact,  the  summit  of  the  moun- 
tain appeared  perfectly  perforated,  and  lava  seemed  to 
ooze  through  its  whole  surface.  As  expressed  by  Palmieri, 
"Vesuvius  sweated  fire."  In  the  daytime  the  cone  ap- 
peared momentarily  covered  with  white  steam  jets  (fuma- 
roles)   which   looked   like  flakes   of    cotton   against   the 


I 


20 


VOLCANOES   OF   NORTH   AMERICA 


^ii: 


■' 


:  i 


■  1 1 


!| 


dark  iiKJuntain  side,  appearing  and  disappearing  at  brief 
intervals. 

Simultaneously  with  the  grand  Assuring  of  the  cone, 
two  large  craters  opened  at  the  summit,  discharging  with 
a  dreadful  noise,  audible  at  a  great  distance,  an  immense 
cloud  of  steam,  dust,  lapilli,  and  bombs.  Volcanic  bombs 
are  masses  of  plastic  lava  hurled  into  the  air  by  the  out- 
rushing  steam  and  acquiring  a  spherical  shape  by  reason 
of  their  rotation.  The  material  thus  projected  into  the 
air  reached  an  elevation  of  nearly  4000  feet  above  the 
sunmiit  of  the  mountain.  It  has  been  computed  that 
the  initial  velocity  of  these  projectiles  must  have  been  in 
the  neighborhood  of  600  feet  per  second. 

The  igneous  period  of  the  eruption  was  short,  for  on 
the  morning  of  the  27th  the  lava  stream  which  flowed 
toward  Resina,  after  covering  a  few  cultivated  fields, 
stopped;  the  lava  descending  from  the  summit  of  the 
mountain  southward,  toward  Camalcloli,  three  miles  and 
a  half  east  of  Resina,  also  ceased  to  flow ;  and  the  great 
lava  torrent  which  passed  the  Observatory  was  lowered 
by  the  onward  flow  of  its  central  portion,  leaving  the 
hardened  sides  standing  like  two  parallel  embankments. 

The  lava  flows  having  ceased  on  the  evening  of  the 
27th,  the  dust,  lapilli,  and  larger  projectiles  became  a 
little  more  abundant,  whilst  the  roaring  noises  of  the 
craters  apparently  became  greater.  The  pine-tree  cloud 
that  rose  from  the  summit  of  the  mountain  was  of  a 
darker  color,  and  was  furrowed  by  lightning  flashes  which 
were  visible  by  daylight  from  the  Observatory,  where  the 
thunder  that  followed  the  flashes  was  heard  usually  after 
an  interval  of  about  seven  seconds. 

On   the   28th  the   dust  and   lapilli   continued   to  fall 


CHARACTEIMSTICS   OF    VOLCANOES 


21 


■ 


abundantly,  darkening  the  air,  and  the  terril)le  noise,  due 
largely  to  the  steam  escaping  from  the  crater,  continued 
with  scarcely  any  diminution. 

On  the  29th,  with  a  strong  wind  blowing  from  the  east, 
scoria  of  such  size  fell  at  the  Observatory,  that  the  glass 
of  the  windows  was  broken.  The  noise  from  the  crater 
continued,  but  the  projectiles  rose  to  a  less  height,  indi- 
cating a  diminution  in  the  power  of  the  eruption. 
Toward  midnight  the  noise  of  the  craters  was  no  longer 
continuous,  and  recurred  with  less  force  and  for  shorter 
intervals.  Almost  at  the  same  hour,  a  tempest  burst  over 
the  region  with  loud  thunder,  but  accompanied  by  little 
rain.  The  disasters  so  frequently  occurring  during  the 
outbursts  of  Vesuvius,  due  to  the  heavy  rains,  which, 
mingling  with  the  loose  dust  and  lapilli,  cause  torrents  of 
mud  to  sweep  down  the  mountain's  sides,  thus,  happily^ 
were  averted. 

On  the  30th  the  detonations  from  the  crater  were  few, 
and  the  steam  issued  only  at  intervals.  By  the  1st  of 
May  the  eruption  was  entirely  over. 

During  the  eruption  earthquake  shocks  caused  the 
Observatory  to  oscillate  continuously,  and  were  felt  not 
only  in  the  adjacent  territory,  but  as  far  as  Montovi. 

The  great  quantity  of  lapilli  which  fell,  buried  the 
scoria  composing  the  upper  portion  of  the  cone  of  Vesu- 
vius and  made  the  ascent  to  the  summit  difficult.  Palnii- 
eri  states  that  having  reached  the  top,  he  found  a  large 
crater  divided  into  two  parts  by  what  seemed  a  cyclopean 
wall.  The  cwo  abysses  had  vertical  sides,  and  revealed 
the  fact  that  the  cone  was  composed  of  alternating  beds 
of  scorial  and  compact  lava.  The  vertical  depth  of  the 
craters  was  approximately  750  feet. 


\l 


Ji. 


lit   ,li^»MI|Mft 


22 


VOLCANOES   OF   NOUTH    AMEIIICA 


m 


M 


H 


i 


A  remarkable  feature  of  the  eruption,  and  one  that  has 
been  observed  in  a  few  otlier  instances,  was  that  not  only 
the  cone  of  Vesuvius,  but  the  whole  adjacent  country 
appeared  white  for  many  days  as  if  snow-covered.  This 
was  due  to  the  connnon  salt  contained  in  the  dust  and 
lapilli  with  which  the  region  about  the  mountain  was 
strewn. 

The  amount  of  molten  rock  outpoured  during  this  erup- 
tion covers  an  area  of  about  one  and  eight-tenths  square 
miles,  with  an  estimated  average  depth  of  thirteen  feet. 
Of  the  amount  of  dust  and  lapilli  scattered  far  and  wide 
and  of  the  volume  of  steam  and  other  gases  discharged, 
not  even  an  approximate  estimate  can  be  made. 

From  the  account  just  given,  it  will  be  seen  that  one  of 
the  most  important  features  of  a  volcanic  eruption  is  the 
transfer  of  material  in  a  solid,  liquid,  or  gaseous  form, 
from  deep  below  the  surface  of  the  earth  to  its  exterior. 
Whence  the  heat  that  liquefied  the  lava,  and  whence  the 
force  tlint  raised  it  to  the  surface? 

The  history  of  Vesuvius  shows  that  it  is  characterized 
by  alternating  periods  of  repose  and  of  activity;  the 
former  being  measured  by  years  and  even  centuries,  the 
latter  by  days  and  even  hours.  The  long  periods  of  mild 
activity  similar  in  character  to  the  normal  condition  of 
Stromljoli,  or  of  complete  inactivity  when  the  mountain 
summit  is  cold  and  silent,  are  broken  by  explosive  par- 
oxysms of  which  the  eruptions  of  79  and  1872  are  illus- 
trative. The  great  majority  of  the  volcanoes  of  the 
world  belong  to  the  Vesuvian  tj'pe. 

Krakatoa.  —  While  Vesuvius  by  reason  of  its  long 
history  and  the  care  with  which  it  has  been  studied,  is 
taken  as  the  type  of  explosive  volcanoes,  its  most  disas- 


\\ 


CUAIIACTEIIISTICS   OF    VOLCANOKS 


28 


troiis  eruptions  sink  into  comparative  insignificance  beside 
the  mighty  expk).sion  that  occurred  in  a  volcano  Icnovvn  as 
Kral^atoa,  in  1883.^  Krakatoa  is  situated  on  a:?  ishmd  of 
the  same  name  in  the  Strait  of  Sunda,  between  Java  and 
Sumatra. 

The  eruption  of  Krakatoa  was  the  most  appalling  out- 
break of  its  kind  that  has  occurred  in  modern  times,  and, 
although  of  the  same  general  character  as  the  eruptions 
characteristic  of  Stromboli  and  Vesuvius,  was  so  tre- 
mendous, and  its  effects  so  disastrous  and  so  wide- 
reaching,  that  it  is  difficult,  if  not  impossible,  for  one 
to  form  a  conception  of  what  took  place. 

Like  Vesuvius  previous  to  the  great  eruption  of  79, 
Krakatoa  was  dormant  and  overgrown  with  vegetation, 
when  the  now  memorable  explosion  occurred.  Previous 
to  the  eruption,  the  island  of  Krakatoa  was  occupied  by 
three  mountain  groups;  the  highest  summit,  that  known  as 
Krakatoa,  being  2622  feet  above  the  sea.  All  of  these 
mountains  were  of  volcanic  origin,  and  bore  evidence  of 
the  occurrence  of  vast  explosive  eruptions  in  prehistoric 
times.  The  only  known  outbreak  previous  to  the  one 
described  below,  took  place  in  1680. 

The  eruption  of  1883  consisted  of  a  series  of  violent 
explosions  which  occurred  from  August  26  to  28,  the 
most  formidable  being  about  seven  on  the  morning  of 
the  27tli.  This  was  the  grand  culmination  of  a  series 
of  minor  explosions  accompanied  by  earthquakes,  which 
began  four  months  previously,  on  the  morning  of  May  30. 
The  noise  of  these  premonitory  disturbances  was  heard  at 

1  A  detailed  report  of  this  eruption  by  a  committee  of  the  Royal  Society 
has  been  published  with  the  title,  "  The  Ei  -iption  of  Krakatoa,  and  Subse- 
quent Phenomena,"  by  Triiber  &  Co.,  London,  1888.  A  quarto  volume  of 
494  pages  and  numerous  maps  and  plates. 


Ji 


'Ml 


II.  ( 


I 


24 


VOLCANOES   OF   NOllTH   AMEUICA 


1      il> 


Batavia  and  other  points  more  than  a  hundred  miles  from 
the  scene  of  the  outbreak.  It  became  known  to  the  in- 
habitants of  Java  and  Sumatra  that  an  erui)tion  of  marked 
violence  was  in  progress  on  the  island  of  Krakatoa,  but  it 
was  not  until  Sunday,  August  26,  that  the  demoi»strations 
became  alarming.  A  little  after  noon  on  that  day,  a 
rumbling  noise,  accompanied  by  short,  feeble  reports,  was 
heard  at  Batavia,  100  miles  east  of  Krakatoa,  and  at 
other  localities  equally  distant.  Those  sounds  increased 
during  the  night,  and  at  seven  the  next  nioining  there 
came  the  most  appalling  crash  of  all.  The  sky  over  the 
Strait  of  Sunda  and  the  bordering  coasts  became  darkened 
by  the  vapor  and  dust  blew  into  the  air,  and  the  dark- 
ness increased  until  the  blackness  of  midnight  ensued. 
Showers  of  dust  began  to  fall.  Repeated  earthquakes 
occurred,  and  loud  explosions,  like  the  discharge  of  heavy 
guns,  were  heard  the  almost  incredible  distance  of  2267 
miles  from  the  scene  of  action. 

One  of  the  nearest  witnesses  of  the  eruption  was  Captain 
Watson,  commander  of  the  British  vessel,  Charles  Bal, 
which  was  ten  miles  south  of  the  island  of  Krakatoa  on 
the  Sunday  afternoon  when  the  volcano  entered  on  its 
greatest  series  of  paroxysms.  The  island  was  shrouded 
in  a  vast  black  cloud,  and  sounds  like  the  discharge  of 
heavy  guns  were  heard  at  intervals  of  a  second  of  time, 
and  accompanied  by  a  crackling  noise  thought  to  have 
been  due  to  the  colliding  of  rock  fragments  in  the  air. 
A  rain  of  pumice,  the  larger  pieces  still  quite  warm,  fell 
on  the  ship. 

It  has  been  estimated  that  the  column  of  steam,  dust, 
and  lapilli  that  rose  above  Krakatoa,  corresponding  with 
the    pine  tree  of  Vesuvius,  attained   a  height   of   from 


J.^- 


CIIAKACTEUISTICS   OF    VOLCANOES 


25 


twelve  to  s(3vcntecn  miles,  and  by  8ome  observers  was 
estimated  to  liave  been  twenty-tbree  miles  in  altitude. 
From  its  widely  expanded  summit  a  rain  of  dust,  lapilli, 
and  fragments  of  i)umice  descended  on  tbe  sea  and  islands 
over  a  radius  of  scores  of  miles.  Tbe  finer  particles 
blown  into  tbe  u})per  regions  of  tbe  atmospbere  were 
borne  away  by  air  currents  and  finally  distributed  over 
tbe  surface  of  tbe  entire  eartb.  Tbe  vast  quantities  of 
fine  dust  blown  into  tbe  upper  regions  of  tbe  atmospbere 
caused  tbe  magnificent  sunset  and  sunrise  effects  tbat 
were  witnessed  on  every  continent  for  two  or  tbree  years 
after  tbe  eruption. 

Observers  wlio  saw  tbe  magnificent  spectacle  from  a 
distance  describe  tbe  towering  column  of  steam,  dust, 
and  lapilli,  as  being  momentarily  illuminated  by  ligbt- 
ning  fiasbes.  Tbe  tbunder  tbat  followed  tbese  discbarges 
was  lost  in  tbe  roar  produced  by  tbe  escaping  steam.  At 
niglit,  tbe  canopy  illuminated  by  tbe  ligbt  of  tbe  volcano 
"  resembled  a  blood-red  curtain  witb  edges  of  all  sbades 
of  yellow ;  the  whole  of  a  murky  tinge,  through  which 
gleamed  fierce  flashes  of  lightning." 

The  force  of  the  explosion  within  the  crater  of  Krakatoa 
was  such  as  to  blow  away  half  of  the  mountain  and  a 
large  portion  of  the  island  on  which  it  stood.  At  a  locality 
in  the  central  part  of  the  island  where  a  mountain  rose 
previous  to  the  eruption,  soundings  now  show  a  depth  of 
a  thousand  feet  of  water.  The  geography  of  the  island 
was  thus  greatly  changed,  much  of  tbe  material  of  which 
it  was  composed  being  blown  away. 

There  is  no  room  for  doubting  that  the  eruption  of 
Krakatoa  was  of  essentially  the  same  nature  as  the  less 
violent  explosions  of  Vesuvius  and  Stromboli.     That  is, 


IK 


26 


VOLCANOES   OF  NOUTH   AMKUICA 


i, 


\'' 


; 


If 


the  immediate  or  proximate  cause  of  the  explosion  find  of 
all  its  attending  [)henomena  was  the  escape  of  super- 
heated steam,  or  the  ignition  of  gases  produced  by  the 
disassociaticjn  of  the  elements  of  water.  The  suddenness 
and  violence  with  which  the  steam  escaped  may  be  appre- 
ciated to  some  extent,  by  the  general  account  of  the  erup- 
tion given  above,  but  will  be  better  understood  by  citing 
more  detailed  ol)servations.  As  in  all  explosions,  vibra- 
tions, or  waves,  were  generated  in  the  surrounding  media. 
In  the  case  of  Krakatoa  these  were  of  three  classes: 
(1)  atmospheric  waves,  (2)  sound  waves,  and  (3)  water 
waves. 

1.  The  atmospheric  waves :  A  large  number  of  bar- 
ometric observations  in  various  parts  of  the  world  have 
shown  thiit  the  atmospheric  wave  generated  by  the  great 
explosion  on  the  morning  of  August  27  expanded  in  all 
directions  until  it  became  a  great  circle,  180°  distant 
from  the  scene  of  the  explosion,  and  then  contracted  to  a 
node  at  the  antipode  of  its  place  of  origin ;  it  then  ex- 
panded and  travelled  back  about  the  earth  to  Krakatoa ; 
whence  it  again  started  on  a  journey  around  the  world  ; 
again  returning  and  again  expanding  and  returning,  ex- 
panding outward  from  its  starting-point  still  again,  it 
travelled  half  around  the  earth  once  more  before  its  ampli- 
tude became  so  reduced  that  it  ceased  to  make  a  distinct 
record  on  self-recording  barometers.  This  remarkable 
phenomenon  of  an  atmospheric  wave  travelling  about  the 
entire  earth  -as  repeated  three  and  a  half  times.  The 
time  required  for  each  complete  excursion  around  the 
earth  was  thirty-six  hours  and  from  twenty-five  to  fifty 
minutes. 

2.  The   sound   wave:    Sounds   like   the   discharge   of 


:sv: 


nrAUACTEUISTICS   OF    VOLCANOKS 


27 


heavy  guns  in  f[uick  succu.ssiori  accoinpaiiiL'd  tho  eruption 
of  Krakatoa,  aiul  woru  hoard,  as  ah'oady  stated,  at  phices 
more  than  2000  miles  distant.  Among  the  numerons 
accounts  sliowing  the  immense  area  over  wliieli  the  sound 
waves  travelled,  puhlished  i)y  the  Committee  of  the  Hoyal 
Society,  are  the  following: 

At  the  Port  of  Acheen,  at  the  northern  extrendty  of 
Sumatra,  distant  1073  miles,  reports  like  the  discharge 
of  cannon  at  sea  were  heard,  and  the  troops  were  put 
under  arms. 

At  Singapore,  distant  522  miles,  two  steamers  were 
despatched  to  look  for  the  vessel  which  was  supposed  to 
be  firing  signal  guns. 

At  Bangkok,  in  Siani,  distant  1413  miles,  the  sound 
was  heard  ;  and  also  at  Labuan,  in  Borneo,  distant  1037 
mills. 

The  discharges  were  also  noted  at  places  in  the  Philip- 
pine islands,  1450  miles  away. 

The  localities  just  mentioned  lie  to  the  northward  of 
Krakatoa.  In  the  opposite  direction  the  noise  was  heard 
at  Perth,  1092  miles  distant,  sounding  like  guns  fired  at 
sea,  and  at  Victoria  Plains,  1700  miles,  in  western  Aus- 
tralia ;  and  Alece  Springs,  2233  miles,  in  southern 
Australia. 

In  a  westerly  direction,  the  sounds  were  heard  at 
Dutch  Bay,  Ceylon,  2058  miles  ;  and  at  the  Chagoz  islands, 
22G7  mile^.  The  last  named  locality  is  the  farthest  from 
Krakatoa  at  which  the  sounds  were  noted. 

Some  idea  of  the  immense  distances  over  which  the 
sound  waves  travelled  may  be  obtained  by  a  comparison 
with  distances  in  North  America.  Had  the  noise  produced 
by  the  earthquake   that  shook  Charleston,  South  Caro- 


r: 


28 


VOLCANOES   OF   NOUTII    AMERICA 


|!i|    I 


I 


i; 


lina,  August  31,  18SG,  Ikumi  as  ^oud  as  those  wliich  accom- 
paniud  tliu  explosion  of  Krakatoa,  —  and  tlie  atuiosjilieric 
and  otlier  conditions  favoring  transmission  been  the 
same, —  it  might  iiave  been  iieard  at  Los  Angeles,  Cali- 
fornia, and  on  the  I'rinee  Kdward  islands. 

3.  Tile  water  wave :  Tiie  eruption  at  Krakatoa,  it 
will  be  rememl)ered,  occurred  on  a  small  island,  and  was 
in  part  subterranean.  A  shock  was  transmitted  to  the 
water  of  the  sea,  which  caused  it  to  rise  and  roll  away  in 
great  waves.  The  largest  of  these  sea  waves,  on  reaching 
the  shores  of  Sumatra  and  Java,  rose  to  a  height  of  fifty 
feet  above  the  normal  water-level  and  caused  immense 
losses  of  life  and  property.^  The  records  of  self-register- 
ing tide-gauges  in  various  countries  show  that  the  waves 
thus  started  travelled  at  least  half  around  the  globe. 

The  brief  summary  of  the  character  and  '  '\»cts  of  the 
eraption  in   the   Strait   of   Sunda  will,  I  'y,  incline 

the  reader  to  agree  with  one  of  our  most  profound 
students  of  volcanic  phenomena,  who  remarks  that, 
while  Vesuvius  is  regarded  as  a  very  ol)streperous  vol- 
canic vent,  its  performances  are  mere  Fourth  of  July 
fireworks  in  comparison  with  the  Day  of  Judgment 
proceedings  of  Krakatoa. 

If  space  permitted,  a  long  series  of  explosive  volcanic 
eruptions  might  be  described,  connecting  the  mild  dis- 
charges of  Stromboli,  which  can  be  watched  with  safety 
at  a  distance  of  a  few  rods,  with  that  of  Krakatoa,  tlie 
effects  of  wliich  in  one  form  or  another  were  felt  over 

1  It  is  stated  by  R.  D.  M.  Verbeek,  in  a  report  on  the  eruption  of  Krakatoa, 
published  by  order  of  the  Governor-General  of  the  Xetherland  Indies,  in 
1886,  that  3fi,y80  human  beings,  including  37  Europeans,  perished,  the 
greater  part  of  whom  were  destroyed  by  the  sea  waves ;  103  villages  were 
entirely,  and  132  partially,  destroyed. 


If 


a^A'a^ftijiiwn  *■»«*«  I  inww») 


riiAiiA(rrKiiisTic8  or  vou'ANoks 


29 


it 


the  entire  earth.  Tlu?  oHmoiiiial  features  in  each  instance 
would  1)0  the  sanu;  ;  the  strikin;^  (liirtTenees  helii*;  in  the 
decree  of  vi(jlence  that  eharacteri/ed  the;  eru[>tit»ns.  The 
mild  explosions  of  Stronil)oli  and  Vesuvius,  as  we  have 
seen,  are  duo  to  the  e8ca[)e  of  the  superheated  stisani. 
The  same  agency  (with  j)rohal)ly  the  added  etTecits  of  the 
ignition  of  oxygen  and  hydrog(>n,  as  will  l)e  considered 
later)  can  he  accepted  as  the  immediate  or  proximate 
cause  of  the  disastrous  explosion  in  the  Strait  of 
Sunda. 

On  a  previous  page  it  was  stated  that  volcanoes  could 
ho  conveniently  divided  into  two  classes,  —  those  that  are 
suhject  to  explosive  eruptions  and  those  which  discharge 
their  lavas  rpiietly.  Let  us  see  what  illustrations  are 
availahle  of  extrusi(  is  of  molten  rock  froni  openings  in 
the  earth's  crust,  which  are  unaccompanied  hy  the  i)yro- 
technic  displays  characteristic  of  Vesuvius,  Etna,  S.'intorin, 
Toneriffe,  Cotopaxi,  Chimborazo,  Conseguina,  Jorullo,  Ori- 
zaba, Fusiyama,  Sumbawa,  and  many  more  —  for  the  vol- 
canoes of  the  explosive  type  far  outnumber  all  others  — 
of  the  world's  most  famous  volcanoes. 

Volcanoes  of  the  Hawaiian  Islands. —  With  the  excep- 
tion of  small  deposits  of  coral  sand,  etc.,  the  Hawaiian 
islands  are  composed  of  rocks  that  were  poured  out  in  a 
molten  condition  from  the  earth's  interior  and  piled  up 
during  successive  eruptions,  until  the  highest  summit 
reached  an  elevation  of  nearly  14,000  feet  above  the  sea. 
The  islajids  rise  from  a  deep  sea.  The  base  of  the  volcanic 
pile  on  the  sea-floor  is  from  15,000  to  18,000  feet  below 
the  ocean's  surface.  Could  waters  of  the  sea  be  with- 
drawn, the  greatest  of  these  volcanoes,  Mauna  Loa, 
would  stand  as  a  mountain  fully  30,000  feet  high,  and 


/ 


w 


lp""li 


I  ^  1'^' 


M 


30 


VOLCANOES   OF   NORTH   AMERICA 


ifil 


3' 


even  exceed  the  elevation  of  the  loftiest  summit  of  the 
Himalay.a  Mountains  ahove  the  present  sea  level.' 

The  Hawaiian  group  consists  of  four  larger  and  four 
smaller  islands.  The  largest  and  most  eitaterly  ot  the 
group,  and  the  only  one  on  which  active  volcanoes  occur, 
is  Hawaii,  which  is  about  ninety  miles  long  by  seventy 
miles  wide,  and  has  an  area  of  approximately  4000 
square  miles. 

One  of  the  most  graphic  accounts  of  the  Hawaiian 
volcanoes,  and  the  one  best  suited  to  the  present  discus- 
sion, is  in  a  published  lecture  on  the  "  Hawaiian  Islands 
and  People "  by  C.  E.  Dutton.^  Much  of  what  follows 
concerning  the  volcanoes  referred  to  is  derived  from 
this  interesting  pamphlet. 

On  the  Island  of  Hawaii  there  are  four  great  volcanoes, 
and  many  smaller  craters  which  are  now  dormant.  The 
southern  half  of  the  island  is  occupied  by  two  grand 
volcanoes,  Mauna  Loa  and  Kilauea.  The  great  central 
pile  is  Mauna  Loa,  the  monarch  among  modern  volcanoes. 
No  other  in  the  world  approaches  it  in  the  vastness  of  its 
mass  or  in  the  magnitude  of  its  eruptive  activity.  Etna 
and  all  its  adjuncts  are  vastly  inferior  ;  while  the  three 
great  volcanic  craes  of  the  Pacific  coast  of  America, — 
Shasta,  Hood,  and  Rainier,  —  if  melted  down  and  run 
together  into  one  pile,  would  still  fall  much  below  the 
volume  of  the  island  volcano. 


1  Many  accounts  of  the  Hawaiian  volcanoes  have  been  published ;  among 
those  most  easily  accessible  to  American  students  are :  "  Hawaiian  Vol- 
canoes" by  C.  E.  Dutton,  in  the  U.  S.  Geological  Survey,  4th  Annual 
Report,  1882-S:{;  and  "Characteristics  of  Volcanoes"  by  J.  D.  Dana,  New 
York,  1890.     The  latter  contains  many  references  to  earlier  publications. 

*  A  lecture  delivered  at  the  U.  S.  National  Museum,  Feb.  9,  ISSl  (sepa- 
rately published),  Washington,  1884. 


:^''. 


CHAUACTERrSTICS   OF   VOLCANOES 


81 


The  summit  of  Mauna  Loa  is  a  moderately  flat  plain 
five  and  a  half  miles  long  and  nearly  four  miles  wide. 
Within  this  plain  is  sunken  a  pit  three  miles  long,  two 
miles  wide,  and  a  thousand  feet  deep.  In  the  floor  of  this 
pit,  at  certain  times,  may  be  seen  a  lake  of  red-hot,  liquid 
lava,  varying  in  size  from  time  to  time,  but  occasionally 
as  large  as  thirty  or  forty  acres.  At  intervals  of  fifteen 
or  twenty  minutes  a  column  of  liquid  lava  of  great  brill- 
iancy is  shot  upwards,  fountain-like,  to  a  height  of  over 
five  hundred  feet,  and  falls  back  into  the  lava  lake  in  a 
fiery  spray.  This  grand  display  is  sometimes  kept  up 
for  months,  and  is  generally  terminated  by  an  eruption. 
'When  an  outbreak  occurs  it  does  not  usually  take  place 
at  the  summit,  but  a  fissure  suddenly  opens  in  the  side 
of  the  mountain,  out  of  which  a  sheet  of  lava  spouts 
hundreds  of  feet  into  the  air,  and  falling,  collects  into  a 
river  of  fire  half  a  mile  in  width.  When  this  occurs,  the 
lava  lake  in  the  crater  subsides,  and  a  vast  cavity  is  left, 
into  which  masses  of  rock  from  the  sides,  previously  sup- 
ported by  the  liquid  lava,  break  away  and  are  precipitated 
with  great  commotion.  This  river  of  molten  rock  rushed 
at  fi'st  with  great  velocity  down  the  side  of  the  mountain. 
After  running  some  miles  it  reaches  more  level  ground, 
when  it  spreads  out  in  great  lakes  or  fields,  and  its  sur- 
face becomes  blackened  as  it  cools  and  hardens.  These 
great  eruptions  take  place  without  explosions  such  as 
characterize  the  outbursts  of  Vesuvius,  but  the  lava  flows 
quietly  out  in  enormous  deluges,  running  sometimes  for 
months,  or  even  a  whole  year,  with  only  the  least  possible 
signs  of  explosive  action  throughout  the  entire  duration 
of  the  flow.  Rarely  are  the  eruptions  accor.ipanied  by 
earthquakes.     So  mild  are  the  discharges  that  an  observer 


82 


VOLCANOES   OF   NORTH   AMERICA 


may  stand  to  the  windward  of  one  of  the  fiery  fountains, 
and  so  near  that  the  heat  will  make  his  face  tingle,  yet 
without  danger.  Usually  the  outbreaks  take  place  with- 
out warning,  and  even  without  the  knowledge  of  the 
people  in  the  vicinity,  who  first  become  aware  of  them  at 
night,  when  the  whole  heavens  are  aglow  with  the  reflected 
light. 

The  great  lava  streams  that  flow  down  the  side  of 
Mauna  Loa  sometimes  attain  a  length  of  nearly  fifty 
miles,  and  occasionally  enter  the  sea.  The  low  angle  of 
slope  presented  by  the  flanks  of  the  mountain,  and  its 
nearly  flat  summit,  are  due  to  the  tendency  of  the  sheet 
of  liquid  rock  to  travel  far  and  spread  widel}'^  before  cool- 
ing. It  is  by  the  successive  addition  of  such  sheets  that 
the  mountain  has  been  built  up.  Nothing  like  the  bombs, 
scoria,  lapilli,  and  ashes,  that  are  piled  about  the  orifices 
of  volcanoes  of  the  explosive  type,  occur.  The  molten 
rock  is  characterized  by  its  liquidity.  It  does  not  retain 
the  occluded  steam  until  a  state  of  extreme  tension  and 
ultimate  violent  explosion  is  reached. 

After  mighty  Mauna  Loa,  the  next  most  interesting 
volcano  on  Hawaii  is  Kilauea,  situated  about  tw^enty-five 
miles  to  the  eastward  and  rising  only  4200  feet  above 
the  sea.  In  the  moderately  flat  summit  of  Kilauea  there 
is  a  pit  or  crater,  about  three  and  a  half  miles  in  length 
and  two  and  a  half  miles  in  width,  nearly  elliptical  in  plan 
and  surrounded  with  cliffs  from  300  to  700  feet  high.  A 
view  of  the  interior  of  this  crater  as  it  appeared  in  the 
summer  of  1883  is  described  by  Dutton,  as  follows :  ^ 

"The  object  upon  which  the  attention  is  instantly  fixed 


■  I 


^ "  Hawaiian  Volcanoes,"  U.  S.  Geological  Survey,  4th  Annual  Report, 
1882-83,  pp.  104,  106. 


CHARACTERISTICS   OF   VOLCANOES 


88 


is  a  large  chaotic  pile  of  rocks  situated  in  the  centre  of 
the  amphitheatre,  rising  to  a  height  which  by  an  eye 
estimate  appears  to  be  about  350  to  400  feet.  From 
innumerable  places  in  this  mass  volumes  of  steam  are 
pouring  forth  and  borne  to  the  leeward  by  the  trade  wind. 
This  pile  of  lava  blocks  is  really  a  cone  of  eruption  with 
a  small  crater  at  the  top.  At  one  side  of  its  base  is  an 
opening  in  the  floor  of  the  main  crater,  within  which  one 
beholds  the  ruddy  glow  of  boiling  lava.  From  numerous 
points  in  the  surrounding  floor  of  the  vast  amphitheatre 
clouds  of  steam  issue  forth  and  melt  away  in  the  steady 
flow  of  the  wind.  The  scene  within  the  great  basin  is 
desolate  and  forbidding  in  the  extreme,  but  upon  the 
summit  of  the  encircling  walls,  and  over  the  outer  slopes 
of  the  mountain,  there  is  a  wealth  of  luxuriant  tropical 
vegetation." 

Descending  the  crater  walls  and  crossing  the  floor  of 
recently  hardened  lava,  from  which  steam  is  issuing 
through  countless  fissures,  one  may  gain  the  border  of 
the  inner  basin  and  look  down  on  the  surface  of  the  pool 
of  molten  rock  that  it  holds.  It  is  to  be  remembered 
that  this  pool  is  really  the  summit  of  a  column  of  liquid 
rock  which  descends  for  thousands  of  feet  into  the  earth. 
Although  red  hot  and  molten  at  the  top,  the  heat  increases 
with  the  depth.  Bubbles  of  steam  are  continually  rising 
through  the  fluid  mass  and  escaping  from  its  surface. 
As  described  by  Button,  this  pool  is  about  480  feet  long 
and  a  little  over  300  feet  in  width.  "  Its  shape  is  reni- 
form,  and  all  about  it  rise  vertical  walls  fifteen  or  twenty 
feet  high.  "When  one  first  reaches  it  the  probabilities  are 
that  the  surface  of  the  lake  will  be  coated  over  with  a 
black  solidified  crust,  showing  a  in  of  fire  all  about  its 


\ 


84 


VOLCANOES   OF   NORTH   AMERICA 


II 


I 


■:i  » 


'       1 


edge.  At  numerous  points  at  the  edge  of  the  crust  jets 
of  fire  are  seen  shooting  upward,  throwing  up  a  spray  of 
glowing  lava  drops  and  emitting  a  dull,  simmering  sound. 
The  heat  for  the  time  being  is  not  intense.  Now  and  then 
a  fountain  breaks  out  in  the  middle  of  the  lake  and  boils 
feebly  for  a  few  minutes.  It  then  becomes  quiet,  but  only 
to  renew  the  operation  at  some  other  point.  Gradually 
the  spurting  and  fretting  at  the  edge  augments.  A  belch 
of  lava  is  thrown  up  here  and  there  to  the  height  of  five 
or  six  feet  and  falls  back  upon  the  crust.  Presently  near 
the  edge  a  cake  of  the  crust  cracks  off,  and  one  edge  of  it 
bending  downward  descends  beneath  the  lava,  and  the 
whole  cake  disappears,  disclosing  a  naked  surface  of 
liquid  fire.  Again  it  coats  over  and  turns  black.  This 
operation  is  repeated  at  other  points  on  the  border  of  the 
lake.  Suddenly  a  network  of  cracks  shoots  through  the 
entire  crust.  Piece  after  piece  of  it  turns  its  edge  upward 
and  sinks  with  a  grand  commotion,  leaving  the  whole 
pool  a  single  expanse  of  liquid  lava.  The  lake  surges 
feebly  for  a  while,  but  soon  comes  to  rest.  The  heat  is 
now  insupportable,  and  for  a  time  it  is  necessary  to  with- 
draw from  the  immediate  brink.  Gradually  the  surface 
darkens  with  the  formation  of  a  new  crust,  which  grows 
blacker  and  blacker  until  the  last  ray  of  incandescence 
disappears.  This  alternation  of  the  freezing  of  the  surface 
of  the  lake  and  the  breaking  up  and  sinking  of  the  crust 
goes  on  in  a  continuous  round,  with  an  approach  to  a 
regular  period  of  about  two  hours." 

For  a  more  extended  account  of  the  quiet  eruptions 
characteristic  of  the  Hawaiian  volcanoes,  I  shall,  for  want 
of  space,  be  obliged  to  refer  the  reader  to  the  highly  in- 
structive reports  concerning  them  already  referred  to. 


i'. 


CHARACTERISTICS   OF   VOLCANOES 


35 


To  imderstand  the  proximate  cause  of  the  l)oiling  of 
the  lakes  of  molten  rock  in  the  summits  of  the  volcanoes 
of  Hawaii,  the  escape  of  steam  from  them,  the  formation 
of  jets  and  fountains  of  fluid  lava,  etc.,  it  is  of  interest  to 
recall  a  homely  comparison  suggested  by  Judd. 

If  a  tall  narrow  vessel  is  filled  with  porridge  or  some 
similar  substance  of  imperfect  fluidity,  and  placed  over  a 
fire,  the  essential  features  of  an  eruption  of  Stromljoli  or 
of  the  boiling  of  the  fiery  lakes  of  Hawaii  may  be  imitated 
in  miniature.  As  the  temperature  of  the  mass  rises, 
steam  is  generated  within  it,  and  in  the  efforts  of  the 
steam  to  escape,  the  substance  is  set  in  violent  movement. 
The  movements  of  the  mass  are  partly  rotary  and  partly 
vertical  in  their  direction;  as  fresh  steam  is  generated  in 
the  mass  its  surface  is  gradually  raised,  while  an  escape 
of  the  steam  is  immediately  followed  by  a  fall  of  the 
surface.  An  up  and  down  movement  is  tlius  maintained, 
but  as  the  generation  of  steam  goes  on  faster  than  it  can 
escape  through  the  viscid  mass,  there  is  a  constant  tendency 
of  the  latter  to  rise  toward  the  mouth  of  the  vessel.  At 
last,  if  heat  continues  to  be  applied  to  the  vessel,  the  fluid 
contents  will  be  forced  up  to  its  edge  and  flow  over,  the 
steam  being  suddenly  and  violently  liberated  from  the 
bubbles  on  the  surface  of  the  mass,  and  a  consideralde 
quantity  of  the  material  forcibly  expelled  from  the  vessel. 
A  stream  of  lava  and  the  hurling  of  fragments  of  liquid 
or  plastic  rock  into  the  air,  as  frequently  happens  in 
Stromboli  and  Vesuvius,  or  the  spouting  of  fiery  spray 
from  the  lava  lakes  of  Hawaii,  are  thus  imitated.  The 
reason  for  the  violent  escape  of  bubbles  of  steam  from  the 
surface  of  boiling  mush, or  at  the  top  of  the  conduit  of  a 
volcano,  is   apparent  when   it   is   remembered   that   the 


1 


86 


VOLCANOES   OP   NORTH   AMERICA 


i'i 


I  ) 


*  )  I 


source  of  heat  is  deep  below  the  surface.  Steam  is  also 
generated  below  the  surface,  but  prolmbly  at  a  moderate 
depth,  and  is  under  the  pressure  of  the  liquid  mass  above, 
and,  besides,  the  viscid  consistency  of  the  material  tends 
to  prevent  the  bubbles  of  steam  from  rising.  But  when 
the  pressure  is  relieved  by  an  overflow  or  by  the  bursting 
of  surface  bubbles,  the  steam  below  has  greater  freedom 
of  escape,  and  rushes  violently  upward. 

The  cause  of  the  explosions  that  occur  in  volcanoes  of 
the  Vesuvian  type,  and  the  spouting  of  lava  fountains  in 
the  lava  lakes  of  Hawaii,  is  the  steam  and  gases  contained 
in  the  molten  material ;  the  variations  in  the  behavior  of 
the  fluid  magma  in  these  contrasted  instances  depend  on 
variations  in  its  consistency.  Lavas  that  are  sufficiently 
heated  are  fluid,  and  boil  without  explosions ;  when  less 
highly  heated  they  are  cohesive,  and  boil  less  freely. 
Lavas  are  also  of  different  composition ;  some  melt  more 
readily  than  others,  and  are  more  fluid  at  the  same  tem- 
perature. Lavas  which  consolidate  quickly  on  a  lowering 
of  temperature  stiffen  at  the  surface,  and  by  resisting  the 
expansive  force  of  the  steam,  which  increases  as  it  nears 
the  surface,  are  ruptured  violently  and  blown  to  frag- 
ments, while  lava  that  does  not  stiffen  so  readily  retains 
its  fluidity  and  allows  the  steam  to  escape  quietly. 

Although  it  is  not  difficult  to  understand  the  conditions 
that  are  immediately  associated  with  volcanic  outbursts, 
the  ultimate  cause  of  the  heat  present,  the  nature  of  the 
force  which  causes  the  lava  to  rise  from  far  below  the  sur- 
face, and  the  sources  of  the  water  that  furnishes  the  steam 
are  more  obscure  phenomena,  which  will  be  considered  in 
advance- 
Fissure  Eruptions.  —  There  is  good  evidence  that  most 


i.i 


CHARACTEIIISTICS   OF    VOLGA  N'OES 


87 


volcanic  eruptions  originate  along  fissures  in  the  earth's 
crust.  The  formation  of  cracks  and  fissures  seems  to  be 
the  cause  of  many  of  the  earth([uakes  that  precede  the 
birth  of  new  volcanoes,  and  also  herald  the  renewal  of 
activity  in  vents  that  have  been  dormant. 

The  study  of  faults,  fissure  veins,  etc.,  has  shown  that 
fissures  in  the  rocks  are  usually  irregular  and  fre(juently 
intersect,  thus  admitting  of  the  escape  of  steam  and  hiva 
with  greater  facility  at  certain  localities  than  at  others. 
In  some  instances,  too,  volcanoes  seem  to  be  located  where 
two  fissures  cross  or  intersect.  An  eruption  once  started 
tends  to  keep  its  conduit  open,  both  on  account  of  the  press- 
ure which  causes  the  magma  to  rise,  and  the  fusion  of 
the  walls  with  which  the  ascending  lava  comes  in  con- 
tact ;  but  when  a  conduit  becomes  closed,  other  openings 
are  frequently  formed  along  the  line  of  the  original  fis- 
sure. Tliis  is  indicated  in  numerous  instances  where  suc- 
cessive eruptions  have  occurred  along  a  w^ell-defined  line  or 
narrow  belt.  A  linear  arrangement  of  volcanoes  has  been 
recognized  in  many  portions  of  the  earth.  An  instance  uf 
this  nature  is  illustrated  on  Plate  8,  which  represents  a 
group  of  beautiful  lapilli  cones,  and  small  lava  flows, 
situated  near  Mono  Lake,  California.  If  this  map  were 
extended  toward  the  northwest  and  southeast,  other  vol- 
canoes along  the  eastern  base  of  the  Sierra  Nevada  would 
be  included,  which  indicates  still  more  clearly  the  inti- 
mate association  of  eruptions  with  a  belt  of  compound 
fractures  and  faults. 

Again,  the  sides  of  great  volcanic  mountains,  like  Etna, 
are  frequently  broken  by  radiating  cracks,  through  which 
lava  escapes  with  the  formation  of  secondary  craters  and 
surface   sheets  of   molten   rock.     The  lava   cooling   and 


.^•w 


38 


VOLCANOES   OF   NOUTH   AMERICA 


I! 


J: 


.1' 

it 


"  >', 


hardening,  in  such  fractures,  foiins  more  or  less  vertical 
sheets  or  dikes,  which  frequently  stand  in  bold  relief  as 
weathering  progresses. 

Should  the  fissures  through  which  molten  rock  reaches 
the  surface  in  what  may  be  termed  normal  volcanic  dis- 
charge, become  more  widely  opened  or  more  numerous,  it 
is  evident  that  the  outpouring  of  lava  might  occur  more 
generally  throughout  their  length.  If  the  lava  was  highly 
liquid,  it  would  spread  out  over  the  land  in  sheets,  without 
building  up  craters  and  mountains,  as  happens  when  the 
energy  of  the  confined  forces  finds  relief  at  a  single  cir- 
cumscribed locality.  Such  an  outpouring  of  liquid  rock 
would  perhaps  be  the  culminating  phase  of  a  series  of 
volcanic  outbreaks  of  less  intensity,  but  would  differ 
from  them  in  its  wider  extent  and  in  the  character  of  the 
topographic  changes  produced,  but  not  in  its  essential 
characteristics. 

Great  inundations  of  lava  of  the  nature  just  considered 
are  known  to  have  occurred,  and  are  designated  asjissure 
eruptions. 

If  we  imagine  quiet  eruptions  of  highly  liquid  lava,  like 
those  that  have  formed  the  broad,  flat-topped  mountains 
of  the  Hawaiian  islands,  to  be  increased  many  thousands 
of  times  in  volume,  and  to  have  reached  the  surface 
through  intersecting  fissures  having  an  aggregate  length 
of  several  hundred  miles,  the  liquid  rock  spreading  in 
widely  extended  sheets  over  the  country,  filling  the  val- 
leys and  giving  a  new  topography  to  the  land,  we  will 
have  what  appears  to  be  the  most  truthful  conception  of 
the  leading  characteristics  of  fissure  eruptions.  If,  after 
one  great  sheet  of  lava  has  cooled  and  hardened,  and  its 
surface   becomes   covered  with   soil   and   vegetation,   or 


CHARACTERISTICS   OF   VOLCANOES 


89 


occupied  in  p.art  by  lakes,  and  dissected  by  streams,  we 
imagine  tlie  lissures  to  be  again  opened  and  to  break 
througli  the  first  formed  layer,  a  second  sheet  of  lava 
might  be  spread  out  over  the  previous  one,  covering  its 
eroded  surface,  and  burying  the  lacustral  and  other  depos- 
its that  had  been  laid  down  on  it  during  the  interval  of 
repose.  Such  a  conception  furnishes  a  mental  picture  of 
what  observations  show  has  taken  place  many  times  in 
certain  large  areas  of  the  earth. 

No  examples  of  fissure  eruptions  of  the  nature  outlined 
above,  can  be  cited  as  having  taken  place  in  historic  times, 
unless  some  of  the  great  lava  flows  of  Iceland  may  be  con- 
sidered as  comparatively  small  illustrations  of  this  method 
of  extrusion.  At  least  two  series  of  widely  spread  lava 
sheets  of  ancient  date,  however,  can  be  shown  to  have 
originated  in  this  manner.  One  of  these  occurs  in  the 
northwestern  portion  of  the  United  States,  and  has  been 
named  the  Columbia  lava;  the  other,  of  about  the  same 
extent,  is  in  India,  and  is  known  as  the  Deccan  trap. 

The  Columbia  lava  covers  an  area  of  between  200,000 
and  250,000  square  miles  in  Idaho,  Oregon,  Washington, 
and  northern  California,  and  is  composed  of  numerous 
sheets,  some  of  which  are  separated  by  lacustral  sediments 
of  Tertiary  age,  and  has  a  maximum  thickness  of  over 
4000  feet.  A  summary  of  what  is  known  concerning 
this,  the  greatest  of  all  the  volcanic  eruptions  of  North 
America,  will  be  presented  in  a  succeeding  chapter.  A 
counterpart  of  nearly  all  its  characteristic  features  occurs 
in  India. 

The  Deccan  Trap.  —  On  the  west  side  of  the  pe  '  isula 
of  India  there  is  a  region  about  200,000  square  miles  in 
area,  where   the  surface   rocks  are   basalt.     Bombay  is 


r' 


40 


VOLCANOES   OF    NOItTII    AMEIIICA 


I 


situated  in  the  central  portion  of  the  western  or  seaward 
margin  of  tliis  iuiiiieuHe  tract. 

The  Deccan  trap  dilfcr.s  from  the  Cohuubia  lava  in  age, 
being  older,  and  belonging  to  the  Cretaceous  instead  of 
the  Tertiary  period.  It  also  differs  from  the  similar  area 
in  America,  in  the  fact  that  the  various  sheets  of  which 
it  is  compo.sed  have  been  but  slightly  disturbed  from  their 
original  horizontal  position.  The  Columbia  lava,  as  will 
be  explained  in  advance,  has  been  broken  throughout 
extensive  areas  by  many  lines  of  fracture,  and  the  blocks 
thus  produced  tilted  and  their  edges  upturned  so  as  to 
form  mountain  ranges. 

The  Deccan  trap,  for  the  most  part,  has  never  been 
covered  by  later  formations,  but  on  account  of  the  great 
length  of  time  it  has  been  exposed,  and  also  because  of 
the  warm  and  humid  climate  of  India,  it  has  suffered  deep 
decay,  and  is  covered  quite  generally  with  a  thick  layer 
of  residual  earth  known  as  laieriie. 

In  the  vicinity  of  Bombay,  the  Deccan  trap  has  a 
thickness  of  over  6000  feet,  but  thins  out  gradually 
eastward.  The  western  portion  of  the  area  is  covered 
by  the  sea,  so  that  its  full  extent  is  unknown.  In  the 
southern  prolongation  of  the  trap  area,  its  thickness  is 
estimated  at  from  2000  to  2500  feet;  in  the  extreme 
eastern  portion,  between  500  and  COO  miles  eastward 
of  Bombay,  the  thickness  in  general  is  but  500  feet. 
The  average  thickness  for  the  entire  area  is  thought  to 
be  about  2000  feet. 

The  Deccan  trap  is  a  dark  basalt  and  consists  of 
many  layers,  some  of  which  are  separated  by  sheets  of 
lacustral  sediment,  and  by  volcanic  lapilli  and  "  ashes." 
Where  the  rocks  beneath  the  basalt  are  exposed,  they  are 


w- 


CIIAUACTKUISTIC'S   OK    VoLCANi  HCS 


41 


found  to  bo  trnverscd  by  dikes.  On  tbo  surfaco  of  tbe 
basalt  tliero  are  no  volcanic  cones  or  crat(M's  of  any  de- 
scription, which  can  Ije  considered  as  niarkinj^  the;  posi- 
tions of  vents  from  which  the  lava  was  extruded. 

In  all  of  these  respects  the  vast  lava-covi'red  area  of 
India  agrees,  ahno.st  to  the  minutest  particulars,  with  the 
conditions  found  to  exist  in  the  region  drained  by  the 
Columbia  River. 

The  facts  just  enumerated  concerning  the  Deccan  trap 
have  been  taken  from  an  admirable  ac(!ount  of  the  geology 
of  India,  by  Oldham.'  A  summary  of  the  observations 
made  on  the  trap  sheets  of  India  contained  in  this  volume, 
might  be  transferred  almost  bodily  to  a  description  of  the 
Columbia  lava.  On  account  of  this  double  interest,  I 
take  the  liberty  of  introducing  it  here  : 

"Recapitulating  the  whole  evidence  [concerning  the 
Deccan  trap],  so  far  as  it  is  presented  to  us  by  the  obser- 
vations hitherto  made,  we  find  that  in  times  subsequent 
to  the  middle  cretaceous,  a  great  area  of  the  Indian  penin- 
sula formed  part  of  a  land  surface,  very  uneven  and 
broken  in  parts,  but  to  the  eastward  apparently  chiefly 
composed  of  extensive  plains,  which,  by  some  slight 
changes  of  level  preceding  the  volcanic  period,  were  con- 
verted into  lakes.  .  .  .  The  lakes  had  apparently  been 
drained,  and  the  deposits,  which  had  accumulated  in 
them,  had  locally  been  subject  to  denudation  before  the 
first  outburst  of  lava  took  place.  These  occurred  at  con- 
siderable intervals,  small  and  very  shallow  lakes  or 
marshes  being  formed  in  the  meantime  by  the  interrup- 
tions  to   the   drainage   produced   by   lava   flows,   or  by 

^  R.  D.  Oldham,  "A  Manual  of  the  Geology  of  India,"  second  edition. 
Calcutta,  1893,  pp.  255-289. 


I  v 


42 


VOLCANOKH   OF   NOUTH    AMKitICA 


cliangca  of  level  iiocompanying  the  volcanic  eruptions. 
In  these  lakes  a  rich  fainia  of  fish,  niolhisca,  entomo.stra- 
coua  Crustacea,  and  water  i)lanta  existed,  whilst  a  varied 
and  probably  a  rich  vegetation  occu|)ied  the  surrounding 
country.  .  .  .  Fresh  flows  of  lava  filled  up  the  first 
lakes,  and  covered  over  the  sedimentary  deposits  which 
had  accumulated  in  the  waters,  but  these  very  Hows,  by 
damming  up  other  lines  of  drainage,  produced  fresh  lakes, 
so  that  several  alternations  of  lava  and  sedimentary  beds 
were  produced  in  places.  Gradually  the  lakes  seem  to 
have  disai)peared,  whether  the  lava  fiows  succeeded  each 
other  so  rapidly  that  there  was  no  time  for  the  accumula- 
tion of  sediments  in  the  interval,  or  whether,  as  is  more 
probable,  the  surface  had  been  converted  into  a  uniform 
plain  of  basalt  by  the  enormous  lava  streams  which  had 
been  poured  out,  it  is  difficult  to  say,  but  no  further 
traces  of  life  have  hitherto  been  found  until  towards  the 
close  of  the  volcanic  epoch.  It  is  possible  that  at  the  end, 
as  at  the  conuuencement  of  the  period,  the  intervals  be- 
tween eruptions  became  longer,  and  the  animal  and  vege- 
table life,  which  may  have  been  seriously  diminished  or 
altogether  driven  out  of  the  country  during  the  rule  of 
igneous  conditions,  resumed  its  old  position,  but  a  great 
change  had  taken  place  in  the  long  interval :  the  old  lacus- 
trine faima  had  died  out,  and  the  animals  and  plants 
which  now  appeared  in  the  country  seem  to  have  differed 
from  those  which  had  formerly  occupied  it.  Lastly,  in 
the  northwestern  portion  of  the  area,  parts  of  the  vol- 
canic country  were  depressed  beneath  the  sea,  and  marine 
Tertiary  deposits  began  to  be  formed  from  the  detritus  of 
the  extinct  volcanoes  and  their  products.  A  great  tract 
of  the  volcanic  region,  however,  appears  to  have  remained 


! 


■ 


CHAltACTEIUSTIC8   OF    VOLCANOES 


48 


! 


tiliiio.st  un(li8turl)(!(l  to  the  prcsi'nt  day,  alToctiMl  l)y  sul> 
aerial  oro.sion  alone,  "ud  never  depr  'sscd  hciieath  tho 
sea  level,  though  probably  for  a  time  at  a  lower  eleva- 
tion than  at  present." 

A  comparison  of  this  aceonnt  of  the  great  basaltic 
sheets  of  India,  with  the  descrijjtion  given  hiter,  of  the 
similar  area  in  Am(M-ica,  will  be  found  instructive. 

Large  porticjus  of  Ai^yssinia  are  reported  to  be  covered 
by  surface  Hows  of  lava,  similar  in  many  ways  to  those  of 
India  and  America,  but  the  evidence  available  concerning 
them  is  not  sufficient  to  show  conidusively  that  they  are 
the  result  of  what  is  understood  as  fissure  eruptions. 

In  some  regions,  also,  as  for  example  the  northwestern 
part  of  the  British  Islands  and  the  adjacent  region  to  the 
northwest,  extending  perhaps  as  far  as  Iceland,  there  are 
extensive  systems  of  dikes,  which  at  one  time,  there  is 
little  doubt,  led  to  extensive  surface  flows.  These  erui)- 
tions  were  so  ancient,  however,  and  the  region  during  its 
subsequent  history  so  situated  in  reference  to  sea  level, 
that  erosion  has  removed  all  or  nearly  all  of  the  surface 
layers,  leaving  only  the  truncated  dikes  that  were  formed 
by  the  filling  of  the  fissures  through  which  the  extruded 
material  found  its  way  to  the  surface.^ 

Trap  Rocks  of  the  Newark  System.  —  In  the  region 
occupied  by  the  Newark  system,  on  the  Atlantic  slope 
of  North  America  and  extending  from  Nova  Scotia  to 
South  Carolina,  there  is  one  of  the  most  extended  series 
of  dikes  and  sheets  of  igneous  rocks  thus  far  discovered. 
The  length  of  this  series  from  northeast  to  northwest  is 


1  Archibald  Geikie,  "  The  Lava-fields  of  Northwestern  Europe,"  in 
"Geological  Sketches  at  Home  aiid  Abroad."  New  York,  1882,  pp.  239- 
249. 


TT 


44 


VOLCANOES   OF   NOUTH   AMERICA 


li: 


about  1000  miles,  and  its  width,  although  its  eastern 
border  is  concealed  by  more  recent  deposits  and  by  the 
sea,  is  not  less  than  200  miles.  The  area  traversed 
by  these  dikes  is  nearly  as  great  as  that  occupied  by  the 
Deccan  trap  or  the  Columbia  lava;  but  unlike  the  regions 
where  those  formations  were  spread  out,  the  Atlantic  coast 
belt  was  an  area  of  both  sedimentation  and  deep  erosion 
during  and  after  the  igneous  invasion.  The  sheets  of 
lava  extruded  at  the  surface  became  in  part  buried  be- 
neath subsecpient  sedimentary  beds,  and  where  erosion 
has  been  least,  still  survive.  In  the  greater  portion  of 
the  area  alonu;  the  Atlantic  coast  that  was  fractured  so  as 
to  admit  of  the  upward  passage  of  molten  rock  from 
beneath,  extensive  and  deep  erosion  has  occurred,  and 
only  truncated  dikes  and  remnants  of  igneous  sheets 
remain.  The  dikes,  in  part,  traverse  rocks  of  Jura- 
Trias  age,  and  their  truncatcil  summits,  in  certain  locali- 
ties, are  buried  beneath  Cretaceous  sediments.^ 

The  several  regions  referred  to  above  furnish  indis- 
putable evidence  that  fissures  have  been  formed  in  the 
earth's  crust,  throughout  great  areas,  during  widely  sepa- 
rated intervals  of  geological  time,  and  that  through  these 
breaks  vast  quantities  ot  molten  rock  have  been  out- 
poured. These,  the  greatest  of  all  eruptions  of  \olcanic 
material  that  have  occurred  since  the  dawn  of  what 
may  be  styled  authentic  geological  history,  have  in  most 
instances  been  accompanied  by  the  formation  of  minor 
quantities  of  projectile  material,  such  as  lapilli,  dust,  etc. 
In  the  main,  the  deluges  of  molten  rock  occurred  without 
the  formation  of  craters  or  pronounced  elevations  of  any 

1  I.  C.  Russell,  "Correlation  Papers  — The  Newark  System."  United 
Statt.^  Geological  Survey.     Bulletin,  No.  85,  pp.  06-77. 


w 


CHARACTERISTICS   OF   VOLCANOES 


45 


kind.  The  layers  occupy  depressions  and  tend  to  subdue 
the  inequalities  in  topography  produced  by  previous  up- 
heavals and  l)y  erosion.  The  rocks  poured  out  during 
fissure  eruptions  are  dark,  heavy,  and,  as  will  be  explained 
in  advance,  are  basic  rocks,  which  fuse  at  a  lower  tem- 
perature than  the  more  siliceous  lavas,  and  when  melted 
are  highly  fluid  and  flow  rapidly,  thus  admitting  of  their 
expanding  broadly  into  thin  sheets. 


Stages  in  the  Lives  of  Volcanoes 

Volcanoes,   like   many   other   features   of    the   earth's 
surface,  have  their  time  of  birth,  periods  of  activity  and 
decline,  terminating  at  last  in  a  time  of  repose,  wdien  they 
become  silent  and  cold.     These  changes  are  less  regular 
and  less  plainly  the  result  of  well-known  laws  than  the 
similar  sequence  of  events  exhibited  by  other  features  of 
the  land,  and  are  apt  to  be  considered,  in  part,  at  least, 
as  of  the  nature  of  catastrophes.     Could  we  take  into 
account,  however,  all  the  forces  that  co-operate  during 
the  varying  phases  of  the  life  history  of  a  volcano,  as,  for 
example,  the  effects   accompanying    the    cooling   r  •;   the 
earth,  the  formation  of  thick  layers  of  sediment  charged 
with  sea  water,  the  manner  in  which  surface  waters  find 
their  way  into  subterranean  regions,  etc.,  it  would  probably 
be  discovered  that  even  volcanoes  which  break  forth  with 
severe  earthquakes,  and  explode  with  such  violence  as  to 
scatter  rock  fragirents  over  half  a  continent,  are  in  reaUty 
the  result  of  slowly  acting  and  finally  culminating  forces 
which  obey  definite  laws. 

However   great   the   diversity  that  volcanoes   display 
during  their  more  active  stages,  there  usually  comes  a 


46 


VOLCANOES   OF   NORTH   AMERICA 


I 


r 


time  in  their  decadence  when  they  heave  marked  simi- 
larities. As  their  energy  declines  they  pass  to  a  state  of 
feeble  activity,  during  which  a  moderate  amount  of  heat 
is  given  off,  accompanied  by  the  escape  of  steam,  carbonic 
acid,  sulphuretted  hydrogen,  and  other  gases. 

The  earlier  portion  of  this  period  of  decline,  when  the 
rocks  are  still  highly  heated  and  at  night  appear  red 
hot  about  the  orifices  from  which  steam  issues  with 
hissing  and  even  a  roaring  noise,  is  termed  the  fmnarole 
stage.  Volcanoes  in  this  condition  emit  sulphurous  and 
hydrochloric  acids  and  less  quantities  of  sulphuretted 
hydrogen  and  carbonic  acid  gas.  About  the  orifices 
when  the  rocks  are  sufficiently  cool,  deposits  of  ulphide 
of  arsenic,  chloride  of  iron,  chloride  of  ammonium, 
boracic  acid,  and  sulphur  are  frequently  formed. 

A  more  marked  decline,  known  as  the  solfaiara  stage, 
is  characterized  by  a  marked  decrease  of  heat  and  a  less 
energetic  escape  of  steam.  The  gases,  in  fact,  as  they 
pass  off,  are  usually  little  if  at  all  above  the  mean  tem- 
perature of  the  atmosphere.  The  type  of  volcanoes  in 
the  solfatara  stage  is  furnished  by  Solfatara,  near  Naples, 
from  which  the  specific  name  is  derived.  From  fissures 
in  tiie  floor  of  the  crater  of  Solfatara  there  issue  contin- 
ually watery  vapors,  sulphurous  acid,  sulphuretted  hy- 
drogen, hydrochloric  acid,  and  chloride  of  ammonium. 
The  action  of  these  substances  upon  one  another,  and 
upon  the  volcanic  rocks  through  which  they  pass,  gives 
rise  to  the  formation  of  certain  chemical  products  which, 
from  a  very  early  period,  have  been  collected  on  account 
of  their  commercial  value.^  The  rocks  surrounding  sol- 
fataras  are  frequently  changed  both  in  color   and   com- 

1  J.  W.  Judd,  "  Volcanoes."    New  York,  1881,  pp.  213,  214. 


CHAKACTEIUSTICS   OF   VOLCANOES 


47 


position  by  the  action  of  the  gases  that  come  in  contact 
with  them. 

In  the  passage  from  the  fumarole  to  the  solfatara 
stage,  the  decrease  in  temperature  is  accompanied  by  a 
change  in  the  nature  of  the  gases  emitted.  Sulphurous 
and  hydrochloric  acids  diminish,  and  the  quantity  of 
sulphuretted  hydrogen  and  carbonic  acid  mingled  with 
them  proportionately  increases. 

When  nearly  all  signs  of  volcanic  activity  have  ceased, 
carbonic  acid  continues  to  pour  forth,  and  being  heavier 
than  the  air,  tends  to  collect  in  low  places,  and  forms 
so-called  poison  valleys,  in  which  insects  and  even  large 
animals  sometimes  perish.  These  manifestations  of  ex- 
piring energy  are  due  mainly  to  contact  of  water  with  the 
hot  rocks,  and  do  not  show  that  a  conduit  leading  to  sub- 
terran-^an  reservoirs  is  still  open.  Fumaroles  and  solfa- 
taras  are  sometimes  found  during  the  early  stages  of 
volcanic  activity,  their  energy  increasing  nntil  explosions 
of  steam  or  eruptions  of  lava  occur ;  the  eruptions  being 
followed  by  long  periods  of  decline,  as  already  stated. 
The  characteristics  of  the  youth  of  volcanoes  are  thus 
repeated  in  what  may  be  termed  ;    second  childhood. 

A  still  later  phase  of  volcanic  energy,  following  the 
solfatai  I  stage,  and  when  gases  no  longer  escape,  is 
marked  by  the  occurrence  of  hot  springs  and  geysers. 
In  regions  covered  with  once  molten  rock,  a  great  lapse 
of  time  is  required  for  the  heat  to  be  conducted  away. 
One  of  the  processes  by  which  this  is  accomplished,  is  by 
the  percolation  of  rain  water  through  the  rocks,  and  its 
emergence  at  the  surface  as  springs.  Water  passes  under- 
ground for  great  distances,  and  also  penetrates  to  a  great 
depth,  not  usually  in  open   passageways,  but   by  perco- 


■) 


48 


VOLCANOES   OF   NORTH   AMERICA 


11  * 


II 


II 


li 


f ; 
I 


* 


lating  through  the  interstices  of  the  rocks  themselves. 
The  residual  heat  of  volcanic  beds  is  thus  abstracted  and 
conducted  to  the  surface.  Fissures  intersecting  the  rocks 
aid  the  escape  of  the  underground  waters.  Fissure 
springs  thus  formed  are  frequently  of  great  volume,  and 
pour  forth  with  temperatures  ranging  from  that  normal 
to  the  rocks  near  the  surface  up  to  the  boiling  point  of 
water,  for  the  elevations  where  they  occur. 

Not  all  hot  springs  owe  their  temperatures  to  the  re- 
sidual heat  of  volcanic  rocks,  however,  since  water  may 
penetrate  to  the  subterranean  regions  that  are  affected  by 
the  general  heat  of  the  earth's  interior  and  again  reach 
the  surface.  The  cooling  of  the  earth  is  greatly  assisted 
in  this  way.  Motion  along  lines  of  fracture  as  where 
faults  are  formed,  or  rocks  are  folded  and  wrinkled,  may 
also  be  transformed  into  heat  by  friction,  and  thus  give 
origin  to  hot  springs  that  are  in  no  way  different,  so  far 
as  their  surface  manifestations  are  concerned,  from  those 
originating  in  other  ways. 

The  three  geyser  regions  of  the  world  are  in  volcanic 
regions,  but  while  geysers,  on  account  of  the  source  of  the 
heat  which  is  the  mainspring  of  the  striking  phenomena 
they  display,  may  be  studied  in  connection  with  the 
subject  before  us,  it  seems  best  to  defer  their  consideration 
and  place  them  in  the  aqueous  rather  than  the  igneous 
branch  of  physiography. 


vl  1    ' 


Characteristics  of  the  Products  of  Volcanoes 

The  matter  emitted  by  volcanoes  may  for  convenience 
be  divided  in  general  into  two  groups ;  namely,  gases  and 
solids.  This  is  perhaps  not  a  scientific  classification, 
since  during  eruptions,  much  of   the   material   included 


T, 


CIIAUACTEUISTICS   OF    VOLCANOES 


49 


among  the  solids  is  poured  out  in  a  liquid  condition ;  and 
some  of  the  gases  and  vapors  are  soon  condensed  into 
solids. 

Gaseous  and  Sublime  1  Products. — Of  all  the  gaseous 
or  vaporous  products  discharged  by  volcanoes,  steam  is 
by  far  the  most  abundant,  and  may  be  considered  as  the 
mainspring,  but  not  the  ultimate  cause,  of  many  volcanic 
phenomena.  No  adequate  measure  of  the  amount  of 
steam  given  off  during  eruptions,  even  of  mild  intensity, 
has  been  made,  but  that  its  volume  is  immense  can  readily 
be  appreciated. 

A  visitor  to  Naples  usually  has  his  attention  attracted 
by  the  "pine  tree"  of  vapor  that  may  almost  always  be 
seen  in  calm  weather,  towering  above  the  summit  of 
Vesuvius.  Observers  agree  that  this  column  is  composed 
almost  entirely  of  the  vapor  of  water.  During  all  stages 
in  the  activity  of  Vesuvius  in  recent  centuries,  this  cloud 
has  hung  over  the  mountain,  at  times  rising  thou- 
sands of  feet  before  expanding,  and  at  other  times,  when 
the  wind  is  strong,  drifting  away  so  as  to  resemble  the 
cloud  banners  so  frequently  to  be  seen  about  Alpine 
summits.  Day  and  night,  and  year  after  year,  this  great 
volume  of  steam  has  been  pouring  out  of  the  crater,  as  if 
it  was  an  immense  boiling  caldron  —  which  in  fact  it  is. 
When  the  activity  increases,  the  steam  issues  under  great 
pressure  and  with  a  roar  that  can  be  heard  for  many 
miles.  The  vapor  column  then  becomes  vastly  enlarged 
and  sometimes,  on  condensing,  causes  heavy  rainfalls;  thus 
demonstrating,  on  a  grand  scale,  that  it  is  the  vapor  of 
water  which  makes  the  mountain  an  object  of  dread. 

It  has  been  computed  by  Fouque,  that  one  of  the 
numerous    parasitic    cones    on    the    lava    flows    of    Etna 


60 


VOLCANOES   OF   NORTH   AMERICA 


•i 


emitted  sufficient  steam  during  one  hundred  days  to 
form  402,000,000  gallons  of  water  if  condensed.  All  of 
the  steam  emitted  by  the  numerous  parasitic  cones  about 
that  great  volcano,  however,  if  combined,  would  fall  far 
short  of  the  amount  that  escapes  from  its  central  crater. 

The  quantity  of  steam  that  escapes  from  volcanoes  after 
they  have  passed  to  the  condition  of  fumaroles  and  solfa- 
taras,  is  still  immense.  In  numerous  examples  like  Sol- 
fatara  and  Volcano,  steam  has  been  continuously  emitted 
for  centuries,  with  a  roar  like  that  produced  when  an 
ocean  steamer  reaches  her  moorings  and  the  safety  valves 
are  opened. 

Not  only  Vesuvius  and  Etna,  but  probably  every  other 
volcano  that  has  been  seen  in  action,  emits  steam  which 
is  derived  from  subterranean  sources.  From  what  is  now 
taking  place  at  hundreds  of  vents,  it  is  safe  to  conclude 
that  all  the  volcanoes  that  have  existed  on  the  earth 
throughout  its  geological  history  have  been  accompanied 
by  the  escape  of  steam  from  within  the  earth's  crust. 

Among  the  numerous  questions  which  the  observation 
of  volcanoes  had  suggested,  one  of  the  most  important  is 
whether  the  steam  they  emit  is  derived  from  water  pres- 
ent in  the  earth  from  the  time  it  became  a  planet,  or  is 
the  supply  furnished  by  the  descent  of  water  from  the 
surface  ?  It  is  my  intention  to  leave  theoretical  discus- 
sions until  the  student  has  made  some  advance  in  obser- 
vation, but  the  analogy  between  volcanoes,  geysers,  and 
springs,  as  well  as  the  study  of  volcanoes  themselves, 
suggests  an  immediate  answer  to  this  query,  to  the  effect 
that  it  is  surface  water  which  supplies  the  steam. 

Of  the  gases  and  vapor  emitted  by  volcanoes,  it  has 
been  estimated  that  nine  hundred  and  ninety-nine  parts  in 


pcgcrarz' 


CHAUACTEUISTICS   OF   VOLCANOES 


51 


a  thousand  consist  of  steam.  Of  the  siil)stances  given  off 
in  a  gaseous  condition  with  the  steam,  the  most  ahundant 
is  usually  sulphurous  acid.  Chlorine  is  also  present 
and  gives  origin  to  hydrochloric  acid ;  it  is  the  pungent 
fumes  of  this  acid  which  frequently  makes  a  near  approach 
to  the  crater  of  Vesuvius  impracticahle.  Snli)huretted 
hydrogen  is  also  emitted,  and,  being  inflanunable,  some- 
times burns  with  a  bluish  flame.  With  the  exception  uf 
flames  of  burning  hydrogen,  noted  below,  this  is  nearly 
always  about  the  only  actual  burning  that  accompanies 
volcanic  eruptions,  and  is  of  decidedly  minor  importance 
as  a  part  of  the  spectacle  witnessed.  The  idea  that  a 
volcano  is  a  "  burning  mountain  "  originated  from  seeing 
the  glow  of  molten  lava  which  is  frequently  reflected  on 
the  clouds  of  steam  above  a  crater. 

Hydrogen  has  also  been  found  in  volcanic  gases.  From 
observations  made  by  Siemens,  at  Vesuvius  in  1878,  as 
stated  by  Geikie,'  it  was  concluded  that  vast  quantities 
of  free  hydrogen  and  of  combustible  compounds  of  that 
gas  exist  dissolved  in  the  magma  of  the  earth's  interior, 
and  that  these  rising  and  exploding  in  the  funnels  of 
volcanoes  give  rise  to  detonations  and  clouds  of  steam. 
When  the  source  of  the  water  which  furnishes  the  steam 
of  volcanoes  is  considered,  it  will  be  found  that  it  is  not 
necessary  to  consider  that  the  free  hydrogen  given  off  by 
volcanoes  is  necessarily  derived  from  the  earth's  interior, 
as  just  stated,  as  it  may  arise  from  the  dis.^ociation 
of  descending  surface  Avater  on  coming  in  contact  with 
ascending  lavas.  At  the  eruption  of  Santorin,  in  18G6, 
hydrogen  was  distinctly  recognized  by  Fouque,  who  for 
the  first  time  established  the  existence  of  true  volcanic 

1  Archibald  Geikie,  "Text-book  of  Geology,"   2d  edition,  1885,  p.  183. 


I 


52 


VOLCANOES   OF    NORTH    AMERICA 


If 


I 


fltiineH.  These  flames  were  again  studied  spectroscopi- 
cally  in  the  following  year  by  Janssen,  who  found  them 
to  be  due  principally  to  the  combustion  of  free  hydrogen, 
but  with  traces  of  chlorine,  soda,  and  copper.  Fouquc 
determined  hy  analysis,  that  immediately  over  the  focus 
of  eruption,  free  hydrogen  formed  thirty  per  cent  of  the 
gases  euiitted,  but  that  the  proposition  rapidly  diminished 
with  distance  from  the  active  vents  and  hotter  lavas, 
while  at  the  same  time  the  proportion  of  marsh  gas  and 
carbon  dioxide  rapidly  increased. 

The  gaseous  emanations  collected  by  Fouqu(3  were  found 
to  contain  aljundant  free  oxygen  as  well  as  hydrogen. 
One  analysis  gave  the  following:  Caibon  dioxide  0.22, 
oxygen  21.11,  nitrogen  21.90,  hydrogen  56.70,  marsh  gas 
0.07  =  100.00.  This  mixture  on  coming  in  contact  with 
a  burning  body  at  once  ignites  with  a  sharp  explosion. 
These  observations  lead  to  the  inference  that  the  water 
vapor  emitted  from  volcanic  vents  exists  in  a  state  of 
dissociation  in  the  molten  magma  previous  to  its  erup- 
tion. This  conclusion  is  not  o)dy  interesting  in  connection 
with  volcanic  studies,  but  highly  suggestive  in  reference  to 
our  concejitions  concerning  the  conditions  existing  within 
or  below  the  earth's  crust. 

As  already  stated,  a  decrease  in  volcanic  activity  is 
usually  accompanied  by  a  change  in  the  gases  emitted. 
This  is  not  only  an  increase  in  the  percentage  of  the 
usually  less  abundant  gases,  owing  to  a  decrease  in  the 
volume  of  steam  poured  out,  but  a  variation  in  the  nature 
of  the  gases  with  changing  conditions.  The  nature  of  this 
change  is  believed  to  differ,  however,  in  different  volcanoes. 
In  the  case  of  Vesuvius,  according  to  Sainte-Claire  Deville, 
the  most  energetic  eruptions  are  accompanied,  by  the  dis- 


h>i 


r;:rJ'-'::Lti'-i  iM-^Jt^i^tAm 


mmmsmsm 


CHARACTERISTICS    OF   VOLCANOES 


r)3 


charge  of  clilorino,  and  to  a  loss  oxtent,  by  fluorine  ;  while 
sulphurous  gases  are  evolved  during  periods  of  lessening 
energy,  being  characteristic,  in  general,  of  solfataras, 
while  carbonic  acid  becomes  prominent  in  fumaroles. 

Of  the  great  variety  of  substances  deposited  on  Oie 
cooler  rocks  in  the  vicinity  of  fumaroles  and  solfataras, 
the  following  may  be  enumerated,  but  the  list  is  not 
complete.  Sodium  chloride  (common  salt)  is  sometimes 
abundant,  and  in  the  case  of  Etna  is  said  to  occur  in 
such  rpiantities  as  to  be  of  commercial  importance.  The 
whitening  of  the  country  about  Vesuvius  by  salt  precipi- 
tated from  the  air  during  an  eruption  has  already  been 
noted.  The  common  occurrences  of  saH  in  the  vapors  of 
volcanoes  is  one  of  the  arguments  sometimes  advanced  for 
the  purpose  of  showing  that  eruptions  are  due  to  the 
access  of  sea-water  to  regions  where  rocks  are  highly 
heated.  That  salt  may  be  derived  from  other  sources, 
however,  will  be  shown  later.  Ferric  chloride  is  con- 
spicuous about  many  volcanic  vents,  and  coats  the  rocks 
with  yellow  and  reddish  incrustations  that  are  frequently 
mistaken  for  suli)hur.  Sulphur  also  occurs,  sometimes  in 
large  quantities,  and  in  many  localities  is  of  commercial 
value.  Ammonium  chloride  and  boracic  acid  are  among 
the  products  of  solfataric  action  that  are  of  economic 
importance.  In  addition  to  the  more  common  substances 
just  named,  there  are  found  sodium  carbonate,  sulphate  of 
lime,  specular  iron,  oxide  of  copper,  and  some  rock-form- 
ing minerals.^ 

Liquid  and  Solid  Products. — All  rock  material  poured 
out  of  volcanoes  in  a  highly  heated  and  fluid  or  plastic 

^  For  further  information  concerning  the  gases  ami  vapors  given  out 
by  volcanoes,  consult  J.  W.  Judd,  "Volcanoes,"  pp.  40-44. 


.  ir 


54 


VOLCANOKH   OK    NOUTH    AMKUICA 


.!      I 

I. 


I; 


iK,| 


' 


condition  is  termed  lava,  irrespective  of  its  niincralogical 
or  chemical  composition.  Much  of  the  lava  becomes 
cooled  sullieiently,  however,  before  its  appearance  at  the 
surface,  to  bo  in  a  solid  condition,  but  is  still  hot,  and 
from  its  identity  with  the  liquid  lavas  that  have  cooled  on 
the  surface  is  plainly  of  the  same  origin.  The  term  lam, 
in  fact,  includes  all  of  the  solid  and  molten  products  of 
volcanic  eruptions,  except  the  fragments  sometimes  torn 
off  by  the  volcanoes  of  the  explosive  type  from  the  beds 
through  which  the  extruded  material  passes  in  order  to 
reach  the  surface.  The  fragments  of  limestone  scattered 
over  the  sides  of  Vesuvius  are  examples  of  such  non-vol- 
cauic  intrusions  in  the  midst  of  truly  igneous  material. 
Other  similar  oxami)les  will  be  cited  later  in  connection 
with  a  description  of  the  Mono  craters,  California. 

The  molten  material  hich  rises  in  the  conduit  of  a 
volcano,  but  does  not  reach  the  surface,  although  it  may 
be  of  the  same  mineralogical  and  chemical  composition  as 
that  which  is  actually  extruded,  is  not  usually  termed 
lava.  Rocks  formed  in  this  way  are  called  plutonic 
rocks.  Between  volcanic  rocks  or  lavas  and  plutonic 
rocks,  however,  there  is  no  well-defined  boundary, 
although  more  or  less  marked  physical  and  mineralogi- 
cal differences  result  from  the  conditions  under  which 
they  cool  and  harden.  These  differences  will  be  noted 
on  a  subsequent  page. 

Lava  Streams.  —  At  times  the  column  of  molten  rock  in 
the  throat  or  conduit  of  a  volcano  rises  until  the  crater 
to  which  it  leads  is  filled,  and  an  overflow  takes  place 
across  the  lowest  point  in  the  crater's  rim. 

In  some  instances  a  stream  of  lava  appears  to  form  a 
channel   for   itself   by  melting  the  rocks  over  which   it 


\ 


CirAUACTKUISTIC'H   OK    VOLCANOKS 


65 


flows,  hut  that  tliis  is  of  common  oociirronce  is  doiihtful. 
When  tlio  sides  of  a  volcanic  mountain  are  couiposed  of 
llglit,  incoherent  scoria,  hipilli,  etc.,  sucii  material  may  l)c 
carried  away,  some  of  it  prol)ahly  hcing  fused.  In  this 
way  a  crater  is  souietimes  hreaciied,  and  a  [)()rtiou  of  its 
rim  removed.  Again,  the  pressure  of  the  lava  rising 
within  a  crater  may  he  sufficient  to  rupture  the  walls 
that  confine  it.  The  howl  containing  the  molten  rocks 
is  thus  hroken  and  its  contents  escape. 

A  more  connnon  way  in  which  craters  discharge  their 
hivas  is  hy  the  opening  of  fissures  in  their  sides.  The 
lava  is  thus  drawn  olf  perhaps  at  the  very  hase  of  a 
crater,  leaving  its  rim  unbroken.  The  innnense  pressure 
of  a  column  of  lava  rising  within  a  volcanic  mountain 
greatly  favors  this  mode  of  escape.  In  the  case  of  the 
volcanoes  on  the  Island  of  Hawaii,  the  lava  sometimes 
issues  from  openings  on  the  sides  of  the  mountains  and 
forms  innnense  fiery  fountains,  several  hundred  feet  in 
height,  which  play  for  days  and  even  weeks.  The 
immediate  force  which  causes  these  great  jets  to  rise  is 
the  static  pressure  of  the  molten  rock  at  higher  levels 
within  the  mountains. 

The  behavior  of  a  lava  stream  after  starting  on  its  wav 
down  a  mountain  varies  according  to  its  degree  of  liquid- 
ity, the  stec  pness  of  the  slope,  the  character  of  the  surface 
over  which  it  flows,  etc.  At  times  the  material  is  highly 
liquid  and  flows  almost  like  water;  again  it  is  thick  and 
viscid  and  descends  slowly  even  on  precipitous  slopes. 
This  difference  in  fluidity  is  due  mainly  to  variations  in 
the  composition  of  the  lava  itself,  some  lavas  fusing  more 
readily  than  others,  and  also  to  the  degree  of  heat  that 
affects   it.     With   sufficient   heat   all   known   substances 


66 


VOLCANOES  OF  NORTH   AMEJIICA 


il 


II 


I 


I 


il 


would  beconu!  fluid,  l)iii  the  do^ree  of  lioat  that  will 
cause  certaiu  lavas  to  becoino  highly  fluid  will  produce 
only  a  viscous  condition  in  others. 

Lavas  may  l)c  divided  into  two  somowliat  well-defined 
classes,  in  reference  to  the  amount  of  silica  they  contain; 
namely,  basic  and  aci<l,  as  will  be  dctscribed  more  definitely 
in  connection  with  the  consideration  of  the  classification 
of  igneous  rocks.  The  basic  lavas  are  dark,  heavy  rocks 
rich  in  iron,  and  as  a  rule  are  much  more  easy  of  fusion 
than  the  usually  lighter  colored  lavas,  which  are  rich  in 
silica.  Marked  mineralogical  differences  usually  accom- 
pany the  variations  in  silica,  and,  as  stated  by  Dana, 
the  fusibility  is  not  controlled  so  much  by  the  amount 
of  silica,  as  by  the  nature  of  the  minerals  of  which 
the  rocks  are  composed,  and  especially  by  the  variety  of 
feldspar  present.  In  basalt,  the  most  easily  fusible  of 
volcanic  rocks,  the  feldspar  is  mainly  laboradorite,  which 
fuses  easily.  Augite  is  also  present,  which  is  rich  in  iron, 
and  is  likewise  of  comparatively  easy  fusibility.  When 
basalt  is  melted  but  not  thoroughly  fused,  the  more 
refractory  minerals  it  contains  float  in  the  magma  formed 
by  the  fusing  of  the  feldspar  and  augite. 

As  the  nature  of  the  material  put  in  a  blast  furnace 
determines  the  readiness  with  which  the  charge  may  be 
melted,  so,  in  nature,  the  composition  of  the  fused  rocks 
in  volcanoes  determines  the  readiness  with  which  the  lava 
discharged  will  flow. 

As  already  stated,  the  degree  of  heat  to  which  a  vol- 
canic magma  is  exposed  also  influences  its  liquidity ;  the 
presence  or  absence  of  water  is  again  an  important  condi- 
tion, since  aqueo-igneous  fusion  is  effected  at  a  much  lower 
temperature  than  what  may  be  termed  dry  fusion.     The 


rnATlA(^TKIlISTI''S   OF    VOLCAVOEH 


57 


study  of  tlu;  coiidituMi  in  wliirli  l;iva  rcaclics  tin;  smfaco 
sf'CMiis  to  sliow,  howovur,  that  it  is  variation  in  tlio  conii'o- 
sition  of  lavas  and  in  tiio  amount  of  water  contained  in 
tlioni,  rather  than  variation  in  temperature,  wliicii  con- 
trol the  niarked  contrasts  ohserved  in  their  liiiidity. 

It  has  been  stated  from  what  may  be  termed  casual 
observations,  that  the  lava  flowing  through  tunnels  on 
the  Island  of  Hawaii  sometimes  rushes  alon^  at  the  rate 
of  forty  miles  an  hour.  No  measurements  to  sustain  this 
statement,  how(>ver,  have  been  made.  A  great  surface 
flow  of  lava  on  Hawaii,  in  1852,  advanced  twenty  miles 
in  as  many  days.  Another  stream,  emitted  in  18oU, 
advanced  thirty-three  miles  in  eight  days,  corresponding 
to  an  average  rate  of  four  miles  a  tlay  on  a  mean  slope  of 
one  foot  in  fifteen.  A  stream  about  thirty  miles  long,  in 
1880  and  1881,  advanced  for  nine  months,  on  a  mean 
slope  of  one  foot  in  thirteen,  or  about  live  degrees.^ 

It  needs  no  argument  to  show  that  the  rapidity  Avith 
which  lava  streams  flow  will  depend  largely  on  the  slopes 
of  the  surfaces  they  descend,  since  they  nuist  obey  the 
laws  of  dynamics  as  applied  to  liquids.  Other  conditions 
being  the  same,  the  steeper  the  slope  the  more  rapid  will 
be  the  flow. 

The  topography  of  a  region  over  which  lava  flows  also 
influences  the  shape  of  the  stream  and  the  rate  at  which 
it  will  advance.  For  example,  if  the  sides  of  a  volcano 
are  channelled  by  descending  valleys,  the  lava  gathering 
in  such  depressions  will  be  confined,  thus  diminishing 
radiation  and  admitting  of  a  quicker  and  greater  ad- 
vance than  if  it  should  spread  out  on  a  uniform,  uneroded 
slope. 

1  J.  D.  Dana,  «  Characteristics  of  Volcanoes,"  New  York,  1890,  pp.  238,  239. 


I 


I'l 


>H 


v. 
'i, 


(ill 

I 


'i. 


ti 


68 


VOLCANOES  OF   NORTH   AMERICA 


The  lava  streams  of  the  Hawaiian  islands  are  com- 
posed of  basic  lava,  and,  as  already  stated,  are  highly 
fl'j'd  at  the  time  of  their  extension.  Where  the  descent 
is  somevvhirt  precipitous,  they  flow  rapidly,  and  at  first  are 
almost  as  liquid  as  water,  but  on  reaching  the  base  of  the 
mountain  they  expand  laterally  and  flow  more  slowly, 
owing  in  part  to  a  decrease  of  fluidity  due  to  loss  of 
heat.  The  length  of  these  streams  is  sometimes  between 
forty  and  fifty  miles. 

Acid  lavas,  on  the  other  hand,  are  usually  thick  and 
viscous,  and  flow  sluggishly  even  on  steep  mountain  sides. 
Frequently  a  stream  of  acid  lava  will  cool  and  harden  on 
a  slope  down  which  a  basic  flow  would  plunge  in  a  cata- 
ract of  fire.  The  tendency  of  basic  lavas  is  to  spread  out 
in  thin  sheets,  which  terminate  with  low  frontal  slopes, 
although  a  thin  margin  is  by  no  means  the  universal  rule ; 
while  the  tendency  of  acid  flows  is  to  form  thick  sheets 
with  precipitous,  and  in  some  cases,  almost  overhanging 
cliff-like  margins. 

Tunnels  in  Lava.  —  The  conditions  controlling  the  rate 
of  flow  of  lava  streams  also  influence  various  phenomena 
displayed  by  them  as  they  advance  and  gradually  cool. 
In  the  case  of  highly  liquid  lavas  especially,  the  surface 
hardens,  while  the  stiil  molten  portion  beneath  flows 
on.  When  the  flow  is  rapid,  this  crust  is  usually  broken 
before  it  can  reach  sufficient  thickness  to  support  its  own 
weight,  and  the  cakes  of  hardened  rock  either  sink  and  are 
remelted,  or  are  swept  along  in  confused  piles.  When 
the  advance  is  slow,  or  is  checked  and  starts  again  when 
the  liquid  portion  below  finds  an  escape,  the  hardened 
surface  is  left  as  a  roof  over  the  space  vacated  by  the 
draining  away  of  the  molten  rock  beneath.     Caverns  of 


k^. 


CHARACTERISTICS   OF   VOLCANOES 


5a 


J 


this  nature  are  of  common  occurrence  in  lava-covered 
regions,  and  may  sometimes  be  followed  for  a  mile,  or 
perhaps  several  miles,  although  they  are  frequently 
obstructed  by  the  falling  in  of  portions  of  their  roofs. 
Examples  of  caverns  formed  in  the  way  just  described 
will  be  noticed  in  giving  an  account  of  the  volcanoes 
of  Utah  and  California. 

The  descent  of  heated  waters  into  lava  caverns  some- 
times leads  to  the  formation  of  curious  stalactites,  which 
differ,  however,  from  those  of  limestone  caverns.  A 
study  of  these  peculiar  forms  has  been  made  by  Dana^ 
and  others. 

The  Aa  Surfaces  of  Lava  Streams.  —  The  hardening  or 
fraezing  over  of  lava  streams  while  the  magma  beneath 
is  still  flowing,  leads,  as  already  stated,  to  the  fracturing 
of  the  crust  and  the  displacement  of  the  blocks  thus 
formed.  Under  the  proper  conditions  affecting  the  rate 
of  cooling  and  the  flow  of  the  still  plastic  interior  of  a 
stream,  the  surface  blocks  are  carried  along,  and  when  the 
lava  finally  hardens,  are  left  in  a  state  of  utmost  confu- 
sion. Sometimes  the  blocks  are  piled  in  huge  heaps,  and 
again  the  general  surface,  although  nearly  horizontal,  is 
composed  of  cakes  of  lava  inclined  in  all  directions,  and 
is  all  but  impassable. 

In  the  Hawaiian  islands  surfaces  of  this  description 
occur  over  areas  many  square  miles  in  extent,  and  are 
known  by  the  native  name  Aa.  This  name  has  been 
adopted  into  the  technical  language  of  geology,  and 
found  to  be  useful  in  describing  many  volcanic  regions. 


1  E.  S.  Dana,  "Lava  Stalactites  from  Caverns  in  Mount  Loa  Lava 
Streams,"  in  "  Characteristics  of  Volcanoes,"  by  J.  U.  Dana,  1890,  pp.  332- 
3i2. 


wm 


60 


VOLCANOES   OF    NOKTII    AMERICA 


! 


!    ,  1 


Hiy 


* 
Id;*  U 

T 


Charactoristic  aa  surfaros  occur  on  every  variety  of 
lava,  but  aro  most  pronoiuniod,  perhaps,  on  those  ol  the 
acid  t3'pe.  Wlien  the  flowing  magma  is  but  imperfectly 
fluid,  a  slight  loss  of  heat  leads  to  the  harden irg  of  the 
surface,  and  the  conditions  favoring  to  the  formation  of 
aa  are  soon  reached.  The  surface  sheet  of  frauinents  is 
then  thick,  and,  indeed,  in  some  instances  the  entire 
stre  M  becomes  charged  with  angular  rock  masses,  held 
in  a  still  viscid  magma.  Such  a  stream  on  solidify- 
ing forms  one  variety  of  what  is  termed  a  volcanic 
breccia.^ 

The  fact  that  the  blocks  of  lava  seen  on  aa  surfaces 
actually  floated  on  the  viscid  stream  of  molten  rock  flow- 
ing beneath  them  is  sometimes  shown  by  grooves  and 
striations  on  their  under  surfaces.  As  the  blocks  are 
carried  along  they  grind  against  each  other,  making  a 
harsh  noise.  In  this  respect  partially  congealed  lava 
streams  form  a  marked  contrast  to  the  advance  of  more 
liquid  lavas,  which  under  similar  topographic  conditions 
flow  quietly. 

The  formation  of  aa  on  Hawaii  is  thiis  described  by 
Button  :  '^  "  Ui)on  the  mountain  slopes  the  lava  runs  with 
great  velocity,  and  the  streams  are  correspondingly  nar- 
row. But  when  it  strikes  the  nearly  horizontal  plain 
below,  its  velocity  is  checked,  and  the  liquid  accumulates 
in  great  volume,  becoming  viscous  by  cooling.  Its  flow- 
is  greatly  retarded,  and  yet  the  mass  is  sufficient  to  en- 

'  A  V)reccia  is  a  rock  composed  of  or  containing  anf^ular  fragments.  A 
sedimentary  breccia  consists  of  angular  fragments  of  older  rocks  of  any 
character  cemented  together  by  mud,  sand,  etc.  In  cave  breccia,  angular 
fragments  are  united  by  the  deposition  of  calcium  carbonate,  etc. 

'■*  C.  K.  Button,  *'  Hawaiian  Volcanoes,"  U.  .S.  Geological  Survey,  4th 
Annual  Report,  1882-8;5,  p.  157. 


r. 


m-ratniyraxitn.^ 


CHAUACTEUISTICS    OF    VOLCANOES 


61 


fi 


J 


'1 


able  it  to  move  with  a  slow  motion  analogous  to  that  of 
a  glacier.  Wlion  the  viscosity  of  the  lava  becomes  very 
great,  it  is  in  a  condition  which  enables  it  to  yield  to 
strains  of  a  certain  amount ;  but  if  that  strain  is  exceeded, 
it  is  crushed  and  ground  up.  The  movement  which  takes 
place  at  this  stage  is  partially  a  plastic  yielding,  more  par- 
ticulai'ly  of  the  interior  and  hotter  parts,  and  partly  a 
shattering  and  grinding  up  of  the  outer,  stiffer,  and  colder 
parts.  This  glacier-like  motion,  however,  is  possible  only 
with  very  large  masses  of  the  lava,  which  still  retains  a 
sulllcient  quantity  of  heat  to  maintain  a  plastic  condition. 
Persons  who  have  witnessed  the  movement  of  a  clinker 
field  in  the  last  stages  of  an  eruption  describe  it  as  be- 
ing so  slow  as  to  be  fjuite  imperceptible  until  it  has  been 
watched  for  a  long  time,  and  as  being  attended  with  a 
crunching  noise  which  comes  in  volleys  like  the  report  of 
musketry." 

The  aa  surfaces  of  lava  streams  resend)le  in  some 
respects  the  surfaces  of  northern  ice  flows,  where  blocks 
of  ice  are  ground  together  and  forced  far  up  shelving 
shores  by  the  pressure  of  the  wind  and  of  water  cur- 
rents. 

Although  the  surfaces  of  basaltic  lavas  are  frequently 
rough,  on  account  of  the  method  of  cooling  described 
above,  their  ruggedness  i;.  mild  in  con.i)ar  son  with  the 
surfaces  of  some  acid  lavas,  as  rhyolitic  obsidian,  for  ex- 
ample, which  is  in  reality  a  glass,  and  breaks  witli  shar}) 
points  and  blade-like  «:;i]gL-  An  exanqile  of  this  nature 
is  furnished  by  thr  streams  of  obsidian  on  the  sides  of 
the  jSIoiio  crater,  California.  An  attempt  to  cross  such 
a  field  of  jagged  and  angular  fragments  of  glass  is  peril- 
ous to  life  and   limbs. 


I 


62 


VOLCANOES   OF   NORTH   AMERICA 


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The  Pahoehoe  Surfaces  of  Lava  Streams. — While  the 
surfaces  of  tliick  sheets  of  basalt  arc  l)roken  and  rendered 
rough  and  uneven  in  the  manner  already  described,  thin 
sheets  cool  rapidly  ^vithout  breaking  into  cakes,  but  fre- 
quently become  wrinkled,  owing  to  the  sluggish  flow  of 
the  thickening  magma.  At  times  these  wrinkled  and 
ropy  surfaces  are  smooth,  resembling  somewhat  in  ap- 
pearance the  surface  of  wind-rippled  mud,  and  again  they 
are  scoriaceous  and  rough.  These  variations  depend  on 
the  nature  of  the  lava  and  the  conditions  under  which 
it  cools.  These  wrinkled  surfaces  frequently  form 
swelling  or  oval  masses,  which  overlap  and  merge  with 
another. 

To  this  peculiar  and  characteristic  variety  of  lava  sur- 
face, the  natives  of  the  Hawaiian  islands  have  given  the 
name  Pahoehoe.  Its  appearance  is  thus  described  by 
Button,  in  the  report  just  cited :  ^ 

"  Imagine  an  army  of  giants  bringing  to  a  common 
dumping-ground  enormous  3aldrons  of  pitch  and  turning 
them  upside  down,  allowing  the  pitch  to  run  out,  some 
running  together,  some  being  poured  over  preceding  dis- 
cliargcs,  and  the  whole  being  finally  left  to  solidity.  The 
individuality  of  each  vesselful  of  pitch  might  be  half  pre- 
served, half  obliterated.  The  svu-face  of  the  entire  ac- 
cumulation would  be  embossed  and  rolling,  by  reason  of 
the  multiplicity  of  the  component  masses,  but  each  mass 
by  itself  would  be  slightly  wrinkled,  yet,  on  the  whole, 
smooth,  involving  no  further  impediment  to  progress 
over  it  than  going  up  and  down  the  smooth-surfaced 
hummocks." 

As  the  surface  and  outer  margin  of  a  stream  of  lava 

1  Page  95. 


ri*4it»in  <><»jyj^w»—  .-K^n^Mimu 


^B^S^^ 


CHARACTEUISTICS   OF   VOLCANOES 


63 


4. 


becomos  clogged  with  fragments  resulting  from  its  cool- 
ing and  breaking,  it  advances  slowly,  but  owing  to  rupt- 
ures in  the  thickened  and  hardened  surface,  the  still 
liquid  interior  escapes  from  its  margin  from  time  to  time, 
being  forced  out  by  the  pressure  from  within.  The  mate- 
rial thus  extruded  by  reason  of  its  high  temperature  and 
fluid  condition  flows  rapidly,  spreads  out  in  thin  sheets, 
but  cools  quickly.  Again  taking  the  evidence  of  an  eye- 
witness :  "  Scarcely  is  one  of  these  little  offshoots  of  lava 
cooled  when  it  is  overflowed  by  another  and  similar  one, 
and  this  process  is  repeated  over  and  over  again.  In  a 
word,  pahoehoe  is  formed  by  small  offshoots  of  very  hot 
and  highly  liquid  lava  from  the  main  stream,  driven  out 
laterally  or  in  advance  of  it  in  a  succession  of  small 
belches.  These  spread  out  very  thin,  cool  quickly,  and 
attain  a  stable  form  before  they  are  covered  by  succeeding 
belches  of  the  same  sort." 

The  Scoriaceous  Surfaces  of  Lava  Streams.  —  A  charac- 
teristic of  molten  lava  is  that  it  contains  steam  and  other 
vapors  or  gases  occluded  in  its  mass.  The  rock  is  in  a 
state  of  aqueous-igneous  fusing ;  that  is,  the  presence  of 
water  allows  it  to  become  liquid  at  temperatures  which  in 
the  absence  of  water  would  not  induce  a  tdiange  lo  a  fluid 
condition.  Occluded  steam  expands  v/hen  the  lava  rises 
toward  the  surface  and  pressure  is  relieved,  and  much  of 
it  escapes,  as  is  shown  by  the  clouds  that  form  over  lava 
flows.  The  rapidity  with  which  the  occluded  steam  ex- 
pands depends  not  only  on  the  temperature  and  the  rate 
at  which  pressure  is  relieved,  but  also  on  the  character 
and  condition  of  the  lava.  When  the  lava  is  highly  fluid 
so  as  to  resemble  the  liquidity  of  water,  the  steam  escapes 
readily ;  when  it  is  more  viscous,  the  steam  is  retained, 


04 


VOLCANOES   OF   NORTH    AMERICA 


]V' 


U  I 


1 


'I' 


but  expands  so  as  to  make  the  rock  op^  i  and  scoriaceous 
in  structure.  Acid  lavas,  being  especially  favorable  for 
the  retention  of  the  steam,  are  frequently  expanded  into 
a  light,  frothy  substance,  termed  pumice.  Owing  to 
movements  in  lava  after  steam  cavities  are  formed  in  it, 
the  vesicles  are  frequently  drawn  out  so  as  to  become 
elliptical  or  even  greatly  elongated.  The  more  basic 
rocks,  as  basalt,  are  also  affected  in  the  same  manner, 
and  become  scoriaceous  or  full  of  steam  cavities,  although 
the  process  is  seldom  carried  far  enough  to  produce 
pumice. 

The  formation  of  steam  cavities  in  still  plastic  lava 
may  be  illustrated  by  wliat  takes  place  in.  bread-making. 
The  carbonic  acid  generated  in  dough  expands  and  gives 
the  plastic  mass  an  open,  cellular  structure ;  when  the 
dough  is  hardened  by  baking,  the  cavities  remain,  sepa- 
rated one  from  another  by  thin  partitions.  The  carbonic 
acid  in  the  dough  plays  the  role  of  the  steam  in  still 
plastic  lava,  although  the  expansion  of  the  steam  is  due 
to  relief  of  pressure.  The  lava  which  has  been  thus 
affected,  when  cooled  and  hardened,  has  an  open,  cellular 
structure  similar  to  that  of  bread.  A  lava  filled  with  an 
abundance  of  steam  cavities  is  said  to  be  scoriaceous} 
Variations  in  scoriaceous  rocks  occur,  depending  largely 

^  Igneous  rocks  contiiiiiing  stoaiu  hlchs,  on  cooling  and  even  long  after 
they  have  lost  all  of  their  heat,  become  permeated  with  water  which  perco- 
lates through  them  and  dissolves  some  of  their  mineral  constituents.  The 
material  thus  dissolved  is  in  many  instances  redeposited  in  the  cavities,  which 
thus  become  filled  with  various  minerals.  Of  the  minerals  thus  deposited, 
quartz  is  the  most  common.  When  the  steam  cavities  tare  filled  in  this 
manner,  and  the  rock  is  broken  open,  hard  kernels  resembling  almonds  in 
shape  are  found  in  the  openings.  Such  rocks  are  called  anajf/dnloids.  It  is 
to  be  remembered  that  in  such  instances  the  amygdules  are  of  secondary  ori- 
gin. Agates  are  formed  by  this  process  of  infiltration.  Cieodes  are  similar 
cavities  not  completely  filled. 


It 


1 


CHAllACTERISTICS   OF    VOLCANOKS 


05 


on  the  size  of  the  cavities  and  on  the  thickness  of  the 
walls  between  them.  The  cavities  are  of  various  diame- 
ters, from  a  small  fraction  of  an  inch  up  to  an  inch  or 
two. 

When  the  pressure  to  which  the  steam  in  lava  is  sub- 
jected is  sufficient,  it  is  prevented  from  expanding.  As 
the  steam  escapes,  the  cavities  are  closed  on  account  of  the 
pressure  about  them.  It  thus  happens  that  lava  streams 
become  scoriaceous  on  their  upper  surfaces,  while  within 
they  cool  into  compact,  stony  masses,  without  cavities 
visible  to  the  eye.  A  characteristic  feature  of  thick  lava 
flows  is,  for  this  reason,  the  presence  of  a  scoriaceous  and 
porous  surface  layer,  which  grades  into  compact  rock 
below. 

When  the  lava  is  of  the  proper  consistency,  steam  rises 
from  several  inches,  and  perhaps  several  feet,  below  the 
surface,  and  tortuous  tubes  are  formed.  Again,  the 
passageways  for  the  escaping  steam  may  unite  as  they 
approach  the  surface  and  lead  to  the  blowing  out  of  more 
or  less  material,  and  the  formation  of  parasitic  cones, 
which  have  many  of  the  characteristics  of  true  volcanoes. 
In  fact,  these  parasitic  cones  are  volcanoes  in  miniature, 
and  differ  from  primary  volcanoes  mainly  in  the  fact  that 
the  supply  of  steam  and  molten  rock  is  small  in  amount. 
Parasitic  ccjues  are  sometimes  common  on  lava  flows,  and 
may  reach  a  height  of  even  a  few  hundred  feet  and  have 
craters  at  their  summits.  They  are  commonly  formed  of 
fragments  of  scoriaceous  lava,  and  emit  steam  with  explo- 
sive violence,  but  seldom  give  origin  to  streams  of  molten 
rock. 

The  upper  surfaces  of  lava  streams,  then,  are  character- 
ized by  various  features,  resulting  from   the   maimer  in 


GO 


VOLCANOES   OF   NORTH   AMEIIICA 


:  i^.i! 


ij!)'' 


Ill 


i 


which  the  hiva  cools ;  rough  aa  surfaces  occur  under  cer- 
tain conditions,  smooth  but  wrinkled  and  mannnillary 
surfaces  under  other  conditions  ;  local  concentration  of  the 
escaping  steam  leads  to  the  formation  of  parasitic  cones, 
and  in  most  cases  the  surface  portions  are  open  and 
cellular. 

When  a  sheet  of  lava  is  poured  out  over  the  surface 
of  a  previous  one,  the  plane  of  separation  is  sometimes 
marked  l)y  the  characteristics  just  enumerated,  but  in 
some  instances  of  this  nature  the  scoriaceous  surface  of 
the  older  sheet  seems  to  have  been  fused  by  the  heat 
of  the  superior  layer,  so  that  the  two  flows  arc  cemented 
together  and  the  plane  of  separation  is  indelinite. 

In  the  walls  of  the  canyons  cut  through  the  Columbia 
lava  in  Washington,  Oregon,  etc.,  ten  or  more  separate 
flows  may  be  distinguished,  which  appear  almost  as 
evenly  stratified  as  layers  of  sedimentary  rock,  in  these 
instances,  however,  the  adjacent  layers  of  basalt  are  some- 
times separated  by  sheets  of  fragmental  volcanic  material, 
produced  by  violent  explosions,  and  by  lacustral  sedi- 
ments, as  well  as  by  scoriaceous  surfaces. 

Characteristics  of  the  Bottoms  of  Lava  Flows.  —  As  a 
lava  stream  advances,  especially  during  the  later  stages  of 
its  flow,  when  the  surface  and  margins  are  in  the  condition 
of  aa,  the  blocks  cooled  at  the  extremity  may  be  carried 
under  the  advancing  mass  and  thus  transferred  to  the 
bottom  of  the  sheet.  Outflow  of  liquid  lava  cooling 
quickly  into  pahoehoe  may  become  buried  in  a  similar 
manner.  Scoriaceous  lava  may  thus  occur  on  the  under 
side  of  a  lava  sheet,  as  well  as  on  its  upper  surface. 

Loose  masses  of  rock  lying  in  the  path  of  an  advancing 
lava  stream  may  become  involved  in  its  lower  portion, 


CHAUACTEUISTU'S    OF    VOLCANOK.S 


••I 


and  cracks  and  openings  of  various  forms,  in  tlio  Hour 
over  wliicli  lava  flows,  nw.y  become  filled.  When  lava 
advances  over  mud  or  other  loose  deposits,  they  may 
become  involved  in  the  fused  rock  and  perhaps  melted 
or  greatly  changed. 

The  rocks  over  which  lava  spreads  .ire  usually  altered 
in  color  and  texture  as  a  result  of  heating,  and  frecjuently 
have  minerals  deposited  in  them  by  the  heated  waters  that 
percolate  through  them.  Changes  of  this  nature  are 
embraced  in  what  is  termed  contact  'iuctcu/wrphism.  The 
extent  of  such  metamorphism  varies,  being  only  a  few 
inches  in  some  instances,  and  again,  when  the  thickness 
of  the  cover  of  volcanic  rock  is  no  greater,  reachiijg 
many  feet  and  perhaps  several  yards.  The  principal  con- 
dition controlling  the  extent  to  which  sedimentary  beds 
are  altered  on  account  of  the  flow  of  lavas  over  th<3m,  seems 
to  depend  on  the  amount  of  water  they  contain.  Dry  heat 
induces  only  local  changes;  heat  accompanied  by  moisture 
brings  about  much  deeper  alterations. 

When  lava  flows  over  a  land  surface,  the  soil  is  baked 
and  usually  reddened  by  the  heat ;  if  ponds  of  water  ai'e 
encountered,  steam  explosions  result,  and  may  lead  to  the 
formation  of  parasitic  cones  on  the  surface  of  the  flow, 
and  to  the  formation  of  sheets  of  volcanic  fragments. 
Instances  a"<i  on  record  in  the  case  of  Etna,  where  lava 
flowed  over  cisterns  filled  with  water,  the  steam  escaping 
through  the  lava  caused  the  blowing  out  of  scoria  ami 
lapilli  and  the  formation  of  miniature  cones  of  eruption. 

Lava  streams  s(jmetimes  advance  into  the  sea,  and  may 
be  formed  on  the  sea  bottom  from  submarine  volcanoes. 
The  characteristics  of  the  surfaces  of  such  flows  Avliich 
would    enable    one    to    distinguish    tl^em    from    subaeriul 


r.8 


VOLCANOKS   OF    NOllTH    AMKIMCA 


III 


;f,' 


/ 


I 


'I 


!l 


\ , 


lavas,  liavo  not  boon  dourly  (.letorniiuod.  The  .study  of 
ancient  lava  .shoots  Hooni.s  to  indicato  that  lo.s.s  striking 
dift'orencos  occur  botwoon  subaorial  and  .subii(|uoous  oxtru- 
.sjon,  than  at  lir.st  might  bo  .surniisod. 

The  Crystalline  Structure  of  the  Central  Portions  of  Lava 
Sheets. — As  is  woll  known,  if  t'lisod  .slag,  or  glass,  i.s 
coolod  quickly,  crystals  are  not  dovol()i)od,  but  tho  nias.s 
when  solid  has  a  glassy  or  stony  structure.  When  such 
material  is  coolod  slowly,  however,  crystals  of  various 
minerals  are  formed  in  a  gla.s.sy  ground  ma.ss,  tho  crystals 
being  larger  and  more  perfect  tho  .slower  the  rate  of  cool- 
ing. The  same  principle  holds  good  in  the  cooling  of 
lava.  When  the  lava  is  in  thick  shoots,  the  central  por- 
tions cool  nmch  more  .slowly  than  the  top  and  bottom, 
and  acquire  a  coarsely  crystalline  texture,  while  the  more 
quickly  cooling  portions  above  and  below  are  frequently 
without  crystals  that  are  visible  to  tho  eye,  and  may 
appear  glas.s-like  or  amorphous  in  texture,  even  when 
examined  in  thin  sections  under  tlie  microscope. 

When  rock  cools  from  a  state  of  fusion,  division  pianos 
or  joints  are  frequently  developed,  which  divide  the  hard- 
ened rock  into  prisms.  It  is  then  said  to  have  a  columnar 
structure.  The  central  portions  of  lava  .sheets,  owing  to 
the  slowness  with  which  they  cool,  frequently  become 
beautifully  columnar ;  while  the  more  ra})idly  cooling 
basal  and  surface  portions  are  either  not  jointed  or  are 
broken  in  a  confused  and  irregular  manner  in  many 
directions.  Tho  prisms  or  columns  formed  during  the 
slow  cooling  of  lava  are  many  times  very  regular,  and 
always  have  their  longer  axes  at  right  angles  to  the  cool- 
ing surfaces.  When  a  lava  sheet  is  cut  through  by  stream 
erosion  or   broken   so  that  a  section   is   exposed,   it   fre- 


CMAKArTERIHTrCS   OF    V(»I,('AN()KH 


rto 


(|iU3ntly  presents  the  apix^uninco  (»f  a  loii^^  coloimadt',  (lie 
coliinins  merging  above  and  below  into  jxtrtions  of  tiie 
sheet  wliieli  are  not  conspicuously  jointed.  In  some 
instances  the  central,  columnar  portion  is  IVom  fifty  to 
a  hundred  or  more  feet  thicd-c,  while  the  individual 
columns,  in  most  instances  broken  by  cross-joints,  are 
from  a  few  in(dies  to  eiglit  or  ten  feet,  in  diameter. 
Usually  the  columns  are  six-sided.  Variations  in  all  of 
the  dimensions  mentioned,  however,  are  of  (lommon 
occurrence. 

It  fre((uently  happens  that  steam  lioles  in  lava  sheets, 
extending  from  a  considerable  depth  to  the  surface,  lead 
to  irregularities  in  the  cooling  surfaces,  and  tlu;  resulting 
colunms,  instead  of  being  vertical  and  regulai'ly  formed, 
arc  grouped  about  the  centre  from  which  the  heat 
escapes,  and  radiate  in  all  directions.  Not  infrcipiently, 
too,  they  are  curved  in.stead  of  straight,  and  show  other 
irregulariti'\s. 

The  marked  variations  in  different  porti(jns  of  lava 
sheets  are  of  interest  especially  in  aiding  one  to  inter- 
pret the  appearances  presented  by  ancient  rocks  of  simi- 
lar origin,  and  in  determining  the  character  of  former 
eruptions.  These,  and  other  features  also,  enable  t)ne  to 
distinguish  surface  flow,  or  extruded  sheets,  from  hiyers 
of  molten  rock  forced  in  among  stratified  beds,  and 
termed  intruded  sheets.  The  characteristics  of  intruded 
sheets  will  be  noted  in  describing  the  origin  and  nature  of 
subterranean  igneous  rocks. 

The  Fragmental  Products.  — During  volcanic  eruptions, 
except  of  the  most  quiet  character,  fragments  of  rock  are 
blown  into  the  air  and  distributed  more  or  less  widely 
over  the  surrounding  region.     The  material  thus  blown 


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VOLCAXOES  OF   NORTH   AMERICA 


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out  may  be  divided  into  two  groups :  the  first,  including 
such  portions  as  are  plastic  when  they  fall,  and  the 
second,  such  lava  fragments  as  have  been  torn  off  of  the 
sides  of  the  craters  by  the  violence  of  the  outrushing 
steam,  and  also  the  liquid  lava  which  is  blown  into  the 
air,  but  cools  and  hardens  before  reaching  the  earth. 
This  grouping  is  arbitrary,  as  there  is  no  sharp  division 
between  plastic  and  solid  volcanic  projectiles,  but  is  con- 
venient for  purposes  of  description  and  study. 

An  example  of  the  manner  in  which  liquid  lava  is 
thrown  into  the  air,  is  furnished  \y  the  lava  fountains 
that  play  on  the  surface  of  the  lake  of  molten  rock  in 
the  crater  of  Kilauea.  As  described  by  many  observers, 
columns  of  lava,  almost  as  liquid  as  water,  are  there  shot 
upwards  to  a  height  of  several  hundred,  and  in  some 
instances  of  nearly  a  thousand,  feet.  The  projecting  force 
in  these  and  all  other  similar  instances  is  mainly,  and 
probably  wholly,  steam.  The  molten  rock  falls  before 
cooliuQi;.  The  most  of  it  returns  to  the  boilino;  lake  of 
lava  from  which  it  rose,  but  some  of  the  drops  and  clot- 
like masses  reach  the  floor  of  the  crater  beyond  the  limit 
of  the  lake,  and  on  hardening  form  scoriaceous  masses 
which  add  to  the  accumulations  of  solid  material. 

Driblet  Cones.  —  ^Yllen  the  fountain-like  eruptions  of 
molten  rock  in  Kilauea  are  less  energetic,  and  especially 
when  they  rise  through  fissures  in  the  crust  that  floors 
the  crater,  the  iava  divides  into  drops  and  falls  about 
the  orifices.  The  drops,  being  yet  hot  and  plastic,  adhere 
one  to  another  and  build  chimney-like  piles,  which  Dana 
has  termed  driblet  cones.  These  are  formed  of  scoria- 
ceous, clot-like  masses  which  are  sometimes  nearly  spheri- 
cal.    These  semi-fused  masses  are  piled  one  on  another 


«■ 


CHARACTERISTICS  OF    VOLCANOES 


71 


in  such  abundr.nce  as  to  form  steep  conical  piles,  in  some 
instances  a  hundred  feet  or  more  in  height.  Occasionally 
the  particles  of  projected  lava  are  small  and  descend  in 
showers  of  loose,  smooth-faced,  but  variously  sliaped  bul- 
lets and  granules  about  the  vents. ^ 

The  conditions  most  favorable  for  the  building  of  drib- 
let cones  occur  when  the  lava  is  highly  fluid,  is  projected 
into  the  air  through  small  openings,  and  cools  sufficiently 
to  become  solid  but  yet  plastic  before  falling.  So  far  as 
has  been  reported,  these  conditions  are  found  only  in 
basaltic  craters.  The  usually  thick  and  pasty  consist- 
ency of  acid  lavas  does  not  favor  the  growth  of  such 
piles  of  congealed  projectiles  as  occur  in  the  crater  of 
Kilauea. 

Pele's  Hair.  — The  air  above  the  seething  lake  of  mol- 
ten lava  on  Kilauea  is  sometimes  filled  with  gossamer 
threads  of  glass,  which  are  carried  away  by  the  wind  and 
accumulate  in  large  quantities  on  the  adjacent  cliffs. 
This  substance  is  known  as  Pele's  hair,  in  memory  of  the 
Hawaiian  goddess  of  the  volcanoes.  It  furnishes  a  con- 
•venient  and  suitable  material,  with  which  birds  build  their 
nests. 

The  capillary  threads  of  glass  forming  Pele's  hair 
resembles  the  "mineral  wool"  used  as  an  insulating 
material  for  steam  pipes,  etc.,  which  is  obtained  by  con- 
ducting a  stream  of  molten  slag  in  front  of  a  strong 
steam  jet;  the  slag  is  blown  away  by  the  force  of  the 
steam,  and  separates  into  drops  which  are  drawn  out  into 
hair-like  threads. 

When  individual  threads  of  Pele's  hair  are  examined 


1  J.  D.  Dana,  "  Characteristics  of  Volcanoes,"  New  York,  1890,  pp.  158- 


160. 


72 


VOLCANOKS    OF    NORTH    AMEUICA 


fi<' 


A' 


i 


under  the  microscope,  they  are  not  found  to  be  even  and 
regular.  The  threads  are  often  tubular,  and  sometimes 
branch,  or  two  threads  are  welded  where  they  cross  each 
other.  The  glass  composing  the  threads  and  tubes  is  far 
from  being  pure,  but  contains  rhombic  crystals  of  various 
minerals  as  well  as  air  cavities,  about  which  there  are 
expansions  of  the  enclosing  glass.  The  crystals  were  evi- 
dently floating  in  the  molten  magma  before  it  was  spun 
out.^ 

The  commonly  accepted  explanation  of  the  formation  of 
Pele's  hair,  is,  that  drops  o^  fluid  lava  are  thrown  into  the 
air  during  the  jetting  and  splashing  of  the  boiling  lava,  and 
drawn  out  into  hair-like  threads  by  the  action  of  the  wind. 
Button  states,  however,  that  nothing  of  this  sort  was  to 
be  observed  during  his  visit  to  Kilauea,  and  yet  Pele's 
hair  was  forming  in  great  abimdance.  Wherever  the 
surface  of  the  molten  lava  was  exposed  by  the  breaking 
up  and  sinking  of  the  hardened  crusts  formed  on  it,  the 
air  above  was  filled  with  filaments  of  glass,  even  when 
there  was  no  spurting  or  apparent  boiling  of  the  molten 
material.  The  explanation  of  the  phenomena  offered  by 
Button  is  as  follows  :  ^ 

"  Liquid  L.va  coming  up  from  the  depths  always  con- 
tains more  or  less  water,  which  is  given  off  slowly  and  by 
degrees,  in  much  the  same  way  as  champagne  gives  off 
carbonic  acid  when  the  bottle  is  uncorked.  Water  vapor 
is  held  in  the  liquid  lava  by  some  affinity  similar  to 
chemical   affinity,  and  though  it  escapes  ultimately,  yet 

^  Descriptions  and  figures  of  Pele's  hair  are  given  by  J.  D.  Dana,  "Char- 
acteristics of  Volcanoes,"  pp.  100-161,  who  cites  the  microscopical  studies  of 
C.  Fr.  \V.  Krukenberg. 

"  C.  E.  Dutton,  "  Hawaiian  Volcanoes,"  U.  S.  Geological  Survey,  4th 
Annual  Report,  1882-83,  p.  108. 


I 

7 


I  'I 


CHAnACTEUISTICS    OF    VOLCANOES 


73 


In 


it  is  surrendered  by  the  lava  with  relnctanco  so  lung  as 
the  lava  remains  fluid.  But  when  the  lava  solidifies,  the 
water  is  expelled  much  more  energetically,  and  the  water 
vapor  separates  in  the  form  of  minute  vesicles.  Since 
the  congelation  of  all  siliceous  compounds  is  a  pa'^sage 
from  a  liquid  condition  through  an  intermediate  stage  of 
viscosity  to  final  solidity,  the  walls  of  these  vesicles  are 
capable  of  being  drawn  out  as  in  the  case  of  glass.  The 
commotion  set  up  by  the  descending  crusts  produces 
eddies  and  numberless  currents  in  the  surface  of  the 
lava.  These  vesicles  are  drawn  out  on  the  surface  of 
the  currents  with  exceeding  tenuity,  producing  myriads 
of  minute  filaments,  and  the  air,  agitated  by  the  intense 
heat  at  the  surface  of  the  pool,  readily  lifts  them  and 
wafts  them  away.  It  forms  almost  wholly  at  the  time 
of  the  break-up.  The  air  is  then  full  of  it.  Yet  I  saw 
no  spouting  or  sputtering,  but  only  the  eddying  of  the 
lava  like  water  in  the  wake  of  a  ship.  The  country  to 
the  leeward  of  Kilauea  shows  an  abundance  of  Pele's  hair, 
and  it  may  be  gathered  by  the  barrelful.  A  bunch  of  it 
is  much  like  finely  shredded  asbestos." 

Volcanic  Bombs.  —  During  explosive  volcanic  eruptions 
masses  of  plastic  lava  are  sometimes  hurled  high  in  the 
air,  and  on  account  principally  of  their  irregularities  of 
form,  acquire  a  rotary  motion,  Avhich  tends  to  make  them 
spherical.  These  revolving  masses  commonly  cool  suffi- 
ciently to  harden  before  reaching  the  earth,  and  are  more 
or  less  perfectly  spherical,  but  at  times  are  still  sufficiently 
plastic  when  they  strike,  to  be  flattened  into  oval  cakes. 
Projectiles  of  this  nature  are  termed  volcanic  bombs. 

The  fact  that  volcanic  bombs  rotate  during  their  flight 
through  the  air  is  shown  not  only  by  their  characteristic 


V 


f. 


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74 


VOT^ANOKS   OF   NORTH   AMKUICA 


In 


II 


ball-like  lorms,  bnt  also  by  spiral  ridges  which  sometimes 
converge  towards  op})usite  poles,  thus  showing  the  posi- 
tion of  the  axis  on  vdiich  they  revolved.  Their  internal 
structure  sometimes  furnishes  evidence  sustaining  the 
same  conclusion.  In  an  example  figured  by  Darwin,^ 
there  is  a  well-defined  shell  of  com})act  lava  near  the 
exterior,  having  a  nearly  uniform  thickness  of  about  the 
third  of  an  inch ;  within  is  a  scoriaceous  mass,  in  which 
the  cells  are  largest  at  the  centre  of  the  bomb  and 
decrease  in  size  to  the  inner  surface  of  the  enclosino;  shell. 
Darwin's  explanation  is  that  the  exterior  cooled  rapidly, 
and  did  not  allow  the  steam  it  contained  to  expand,  while 
the  still  plastic  central  portion  cooled  slowly.  Owing 
to  the  centrifugal  force  due  to  rotation,  pressure  was 
relieved  at  the  centre  and  allowed  the  core  of  slowly 
cooling  lava  to  become  cellular. 

The  distance  from  a  volcano  at  which  bombs  may  fall 
must  evidently  depend  not  only  on  their  initial  velocity, 
but  on  the  angle  at  which  they  start  on  their  flight. 
During  an  eruption  of  Cotopaxi,  bombs  were  thrown  a 
distance  of  nine  miles. 

Lava  balls  are  described  by  Dana^  as  occurring  on 
Hawaii,  that  resemble  bombs  in  appearance,  but  owe 
their  form  to  a  rolling  motion  in  the  forward  portion  of 
an  advancing  aa  stream,  due  to  friction  on  the  bottom. 
Certain  so-called  bombs  on  Vesuvius  are  thought  to  have 
a  similiar  origin. 

Scoria   Cones.  —  Lava   not   sufficiently  fluid  to  fall  in 

*  Charles  Darwin,  "  Geological  Observations  on  Volcanic  Islands,"  1814, 
pp.  36,  37. 

''J.  D.  Dana,  "Characteristics  of  Volcanoes,"  pp.  11,  245.  A  reference 
is  given  by  Dana  to  "  The  Fragmentary  Ejectanienta  of  Volcanoes,"  by 
Johnson-Lewis,  in  "  Am.  Jour.  Sci.,"  1888,  Vol.  34,  p.  103. 


? 


CHARACTERISTICS   OF    VOLCANOES 


Tf) 


drops  <as  in  tlie  formation  of  clril)let  conos,  and  not  pro- 
jected with  snfRcicnt  velocity  to  give  origin  to  boin))s, 
frequently  falls  about  a  volcanic  vent  in  thick,  clot-like 
masses  which  are  still  plastic  when  they  reach  the  earth, 
but  more  frequently,  perhaps,  cool  and  harden  into  rough, 
scoriaceous,  slag-like  masses  before  coming  to  rest.  Those 
masses,  of  various  size  up  to  perhaps  a  foot  or  two  in 
diameter  in  many  instances,  accumulate  about  the  orifice 
from  which  they  were  projected  and  build  up  conical 
piles  with  depressions  in  their  summits.  The  "  cone  of 
eruption  "  usually  to  be  seen  within  the  crater  of  Vesuvius 
is  of  this  nature.  Such  cones  are  common  in  most  vol- 
canic districts,  and  may  attain  vast  dimensions.  Scoria 
cones  grade  into  others  formed  of  smaller  projectiles, 
averafjing  about  half  an  inch  in  diameter,  and  termed 
lapilli,  the  term  having  been  adopted  from  the  Italian 
name  for  the  small,  gravel-like  accumulation  of  scoriaceous 
fragments  about  Vesuvius.  Scoria  and  lapilli  are  of  like 
origin,  and  commonly  occur  together  in  the  same  cones ; 
v/hen  the  former  predominates,  a  scoria  or  "cinder"  cone 
results,  and  when  the  latter  is  in  the  greater  abundance, 
lapilli  conos  are  formed. 

Still  finer  projectiles  of  the  same  character  as  lapilli 
pass  under  the  names  volcanic  gravel,  volcanic  sand,  and 
volcanic  dust,  according  to  size.  The  finest  volcanic 
ejectamenta  are  sometimes  termed  volcanic  ashes,  but 
as  this  term  conveys  the  idea  that  they  are  the  residue 
left  by  combustion,  it  is  a  misnomer  and  should  not  be 
used. 

Sheets  of  Volcanic  Sand  and  Dust.  —  In  the  case  of  vol- 
canic eruptions  of  the  explosive  type,  the  steam  occluded 
in  the  lava  expands  as  external  pressure  is  relieved  ;  this 


f: 


76 


VOLCANOES   OF    NOUTII   AMEIIICA 


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expansion  is  frequently  so  violent  that  the  rock  is  disin- 
tegrated and  the  fragments  projected  high  in  the  air.  Be- 
side this  primary  mode  of  reducing  the  lava  to  fragments, 
and  much  of  it  to  the  condition  of  dust,  the  larger  frag- 
ments as  they  are  shot  upwards  with  a  velocity  in  some  in- 
stances even  greater  than  the  initial  velocity  of  shells  fired 
from  modern  rifle-caimon,  strike  against  one  another  and 
against  falling  fragments,  and  are  shattered,  thus  tend- 
ing to  increase  the  quantity  of  fine,  dust-like  particles 
produced.  While  much  fine  material  originates  thus, 
and  is  carried  away  by  the  wind,  many  of  the  fragments 
that  escape  comminution  fall  into  the  crater  from  which 
they  were  thrown  and  are  again  violently  ejected,  thus 
multiplying  the  chances  of  their  being  reduced  to  powder. 
An  eruption  of  the  explosive  type  thus  tends  to  form  much 
fine  dust,  which  is  carried  high  into  the  air  by  the  upward 
rushing  c'team  and  falls  most  abundantly  near  the  place 
of  discharge.  Should  a  strong  wind  be  blowing,  the  dust 
is  carried  to  leeward  of  the  volcano,  and  on  reaching  the 
earth  forms  a  sheet,  which,  owing  to  the  winnowing  action 
of  the  wind,  is  composed  of  finer  and  finer  fragments,  the 
greater  the  distance  from  the  volcano. 

The  wide  distribution  of  the  dust  of  Krakatoa,  which 
was  probably  deposited  over  the  entire  earth's  surface, 
has  already  been  referred  to.  Many  instances  are  on 
record  of  volcanic  dust  falling  hundreds  of  miles  from  the 
parent  volcano.  It  is  not  an  unusual  occurrence  for  ves- 
sels far  out  at  sea  to  encounter  showers  of  volcanic  dust, 
which  whiten  their  decks.  During  the  winter  of  1875-76 
dust  fell  in  Norway  which  was  similar  to  that  previously 
erupted  from  volcanoes  in  Iceland,  and  it  was  predicted 
that  some  volcano  on  that  distant  island  was  in  a  state 


•^  ' 


CHAIIACTEUISTICS   OF    VOLCANOES 


77 


'I* 


of  eruption ;  intelligence  received  several  weeks  later  con- 
firmed the  correctnens  of  this  conjecture.' 

The  steam  clouds  so  frequently  seen  rising  from  vol- 
canoes in  a  state  of  mild  activity  when  illuminated  by  the 
sun  are  of  a  brilliant,  lleecy  white ;  should  the  steam 
explosions  become  more  violent,  the  color  of  the  colunm 
is  frerpiently  changed  to  an  inky  blackness.  Tiiis  is  due 
to  the  vast  quantities  of  dust  and  stones  shot  u})\var(l 
with  the  steam.  A  grapliic  account  of  the  projection 
of  a  dark  cloud  of  volcanic  dust  from  Cotopaxi  on 
July  3,  1880,  is  given  by  Whymper,'-  in  recording  his 
observations  while  on  the  summit  of  Chimborazo : 

"  The  sky  was  bright,  the  air  serene ;  and  long  before 
dawn,  sixty  miles  away,  we  saw  the  cone  of  Cotopaxi 
clear  cut  against  a  cloudless  horizon,  and  remarked  how 
tranquil  the  great  volcano  looked,  and  that  not  a  sign 
of  smoke  was  rising  from  the  crater.  ...  At  5.40  a.m. 
two  puffs  of  steam  were  emitted,  and  then  there  was  a 
pause.  At  5.45  a  volume  of  inky  blackness  began  to 
rise,  and  went  up  straight  in  the  air  with  such  prodigious 
velocity  that  in  less  than  a  minute  it  had  risen  20,000 
feet  above  the  rim  of  the  crater.  I  could  see  the  upper 
10,000  feet  of  the  volcano,  and  estimated  the  height  of 
the  column  at  double  the  height  of  the  visible  portion  of 
the  mountain.  The  top  of  the  column,  therefore,  was 
nearly  40,000  feet  above  the  level  of  the  sea.  At 
that  elevation  it  encountered  a  powerful  wind  blowing 
from  the  east,  and  was  rapidly  borne  towards  the  Pacific, 
remaining  intensely  black,  seeming  to  spread  very  slightly. 


1  J.  W.  .Tudd,  "  Volcanoes,"  p.  72. 

'•^  Edward  Whymper,  "  Travels  amongst  the  Great  Andes  of  the  Equator," 
Xew  York,  1892,  pp.  320-3;i0. 


78 


VOLCANOES   OF   NOUTII    AMEUICA 


i 


\ 


n 


and  prcsuiitiii"^  the  appoaraiico  of  a  gigantic  I,  drawn 
upon  an  otlua-wiso  perfectly  clear  .sky.  It  was  then 
caught  by  wind  from  the  north,  and,  borne  towards  us, 
appeared  to  spread  quickly.  .  .  .  For  a  full  hour  we  saw 
the  innnense  colunni  still  rising  from  the  crater,  and  then 
the  clouds  which  were  drifting  towards  us  shut  it  out. 

"  When  they  connnenced  to  intervene  between  the  sun 
and  ourselves,  the  eflectN  which  were  produced  were  very 
truly  amazing.  We  saw  a  green  sun,  and  smears  of  color 
something  like  verdigris-green  high  up  in  the  sky,  which 
changed  to  equally  extreme  blood-red,  or  to  warm  brick- 
red,  and  then  passed  in  an  instant  to  the  color  of  tar- 
nished copper,  or  shining  brass.  No  words  can  convey  the 
faintest  idea  of  the  impressive  appearance  of  these  strange 
colors  in  the  sky,  —  seen  one  moment  and  gone  the  next, 
—  resembliug  nothing  to  which  they  can  properly  be  com- 
pared, and  surpassing  in  vivid  intensity  the  wildest  effects 
of  the  most  gorgeous  sunsets. 

'"  About  midday  the  cloud  passsd  overhead,  having 
taken  six  hours  to  travel  about  eighty  miles.  The  sun 
then  became  invisible,  and  the  temperature  fell  to  15°  F. 

"  When  the  clouds  from  Cotopaxi  first  passed  overhead, 
they  were  still,  I  think,  not  less  than  5000  feet  above  us 
(or  25,000  to  26,000  feet  above  the  sea),  and  they  extended 
far  to  the  south  before  the  dust  of  which  they  were  com- 
posed began  to  fall  upon  the  summit  of  Chimborazo.  It 
commenced  to  settle  about  ten  minutes  after  our  arrival, 
and  in  the  course  of  an  hour  caused  tlie  snowy  summit 
to  look  like  a  ploughed  field.  It  filled  our  eyes  and  nos- 
trils, rendering  eating  and  drinking  impossible,  and  at  last 
reduced  us  to  breathino;  throuo;h  handkerchiefs." 

This  discharge  of  dust,  as  ascertained  later  by  Whym- 


T* 


CIIAUACTEIIISTICS   OF    VOLCANOEH 


l9 


J 


per,  fell  over  many  huiKlrcds  of  square  inilc?*.  Its  ainoiiiit 
was  estimated  at  not  l(!ss  than  two  millions  of  tons  ;  eipial 
to  a  column  of  solid  lava  (2.G5  speeilic  gravity)  l\H  feet 
S(|uare  and  18,000  feet  liigli. 

Tlic  dust  which  fell  on  the  summit  of  Chimhorazo  was 
examined  microscopically  by  Professor  Bonney,  and  found 
to  consist  of  mineral  and  glass  fragments  from  .02  inch 
in  diameter  downwards. 

Th'i  instructive  erupticjn  from  Cotopaxi  witnessed  by 
Whymper,  although  small  in  comparison  witli  many  dis- 
charges of  dust  that  have  occurred,  enables  one  to  (jbtain 
a  graphic  idea  of  what  takes  place  when  sheets  of  line 
fragments  like  those  which  occur  in  the  far  west,  not  only 
hundreds  but  thousands  of  square  miles  in  area  and  with 
an  average  depth  of  twenty  feet  or  more,  are  deposited 
over  the  land.  The  sheets  of  volcanic  dust  referred  to 
will  be  described  later  in  connection  with  other  volcanic 
phenomena  in  North  America. 

An  interesting  variation  in  the  manner  in  which  steam 
escapes  from  a  volcano  has  been  noted  in  the  case  of  the 
volcano  known  as  Akutan,  on  an  island  of  the  same  name, 
Alaska.  In  calm  weather  immense  rings  or  wreaths  of 
black,  dust-charged  steam  rise  from  the  summit  of  the 
mountain  and  float  away  one  after  another  and  gradu- 
ally expand  as  they  rise.  These  wreaths  appear  to 
be  vortex  rini2;s  similar  to  those  sometimes  blown  out 
of  the  smoke-stack  of  a  locomotive.  Akutan  has  not 
been  closely  examined,  but  apparently  it  has  a  deep  fun- 
nel-shaped crater,  and  the  steam  escaping  from  the  liquid 
lava  deep  within  its  throat  blows  out  dust-charged  steam 
in  the  manner  m  which  vortex  rings  are  found  in  labora- 
tory experiments.     When   the  volcanic  wreaths  are  less 


i  I 


I'lH' 


i  ii 


'M 


m 


A 


rt 


80 


VOI.CANOKS    OF    NOitTM    AMKIUCA 


well  defined,  the  iisceiuliii^  steam  column,  convM|)()ndin;^ 
with  the  pine  tree  of  Vesuvius,  has  what  iii)[)eiii's  to  be  a 
spirally  twisted  trunk. 

PitOFlLKS    OF    Vor.CAXIC    MOUNTAINS 

The  two  varieties  oi  volcanic  eruptions,  the  quiet  and 
the  ex[)losivc,  characterized  respectively  by  the  emission 
of  streams  of  highly  licpiid  lava,  and  the  l)lowing  out  of 
fragments,  lead  to  the  building  of  two  well-marked  types 
of  mountains. 

When  lava  is  poured  out  in  a  highly  liquid  condition, 
it  flows  rapidly,  frequently  reaching  a  distance  of  fifty 
miles  or  more,  and  under  favorable  topographic  condi- 
tions si)reads  out  widely  so  as  to  form  thin  sheets.  A 
succession  of  flows  of  this  nature  from  the  same  vent 
leads  to  the  piling  up  of  layer  above  layer  until  a  moun- 
tain with  a  broad  base  and  gentle  slopes  is  formed.  Of 
such  mountains  Mauna  Loa  may  l)e  taken  as  the  type. 
Its  base  at  sea  level  is  between  fifty  and  sixty  miles  in 
diameter.  The  mean  slope  within  a  circle  of  five  miles 
aljout  the  summit  crater,  as  stated  by  Dana,  is  about 
three  degrees.  At  a  greater  distance  from  the  crater 
the  slope  increases  to  an  average  of  perhaps  five  degrees. 
The  mountain  is  thus  a  flat-topped  dome.  The  reason  for 
the  increase  in  slope  at  a  distance  in  excess  on  an  average 
of  five  miles  from  the  crater,  is  that  the  outbursts  of  lava 
are  usually  from  the  sides  instead  of  the  summit  of  the 
mountain. 

Volcanoes  in  a  state  of  explosive  eruption,  as  we  have 
seen,  project  scoria,  bombs,  lapilli,  dust,  etc.,  high  in  the 
air.  Much  of  this  material  falls  about  the  orifice  from 
which  it  was  thrown  and  builds  u^  a  cinder,  or  lapilli 


■M 


iff 


CIIAUACTEUISTICS   OF    VOJX'ANOES 


81 


cone :  tlic  liir^^(fr  fnij^nnontM  .is  a  rule  fall  near  the  place 
of  eruption,  while  smaller  ones  may  he  carried  a  great 
distance.  When  tlu;  ('rn[)tions  are  long  continued,  coni- 
cal mountains  are  formed  hy  this  process,  the  sides  of 
which  are  steep.  In  many  instances,  their  outer  slopes 
have  an  inclination  of  thirty  to  forty  degrees.  The  angle 
is  determined  hy  the  "angle  of  repo.se"  of  the  material 
of  which  the  C(mes  are  huilt,  and  varies  with  tin;  size  and 
angularity  ot  the  fragments.  Mountains  of  this  type  are 
illustrated    especially    by    Fusiyama,   Japan    (Plate    3); 


PROFILE  OF  SHISHALDIN;  DRAWN  FROM  A  PHOTOGRAPH;  SCALE  ABOUT  10,000  FT.=  \  INCH. 


PROFILE  OF  LOA  AND  KILAUEA;   AFTER  J.  D.  DANA;  SCALE  ABOUT  10  MILES=  1  INCH. 

Via.  2.  Profiles  of  volcanic  mounUins.  Tlio  upper  diaftr'^m  shows  the  characteris- 
tic ontliiio  of  a  cone  resultiiiK  from  mild  explosions  ;  tUo  lower  diagram,  the  form 
produced  by  the  qiiiet  offusiou  of  highly  litiuid  hivii. 

Shislialdin,  on  Unimak  Island ;  and  St.  Augu.stine, 
Cook's  Inlet  (Plate  3),  Alaska.  Nearly  all  of  the  coni- 
cal volcanic  piles  on  the  earth  are  of  this  class,  but  in 
most  instances  the  regularity  of  their  slopes  has  been 
modified  by  overflows,  or  outbreaks  of  lava,  and  by 
erosion. 

Not  only  are  the  sides  of  volcanic  cones  built  of  frag- 
mental  material,  steep,  as  already  mentioned,  but  when 
seen  in  profile  they  present  regular  and  very  beautiful 
curves,  as  may  be  seen  from  the  accompanying  illustration 
of  Fusiyama.     The  reason  for  this  characteristic  curva- 


fj  i' 


82 


VOLCANOES   OF   NOUTH   AMLRICA 


n  '■ 


i 


J' 


lure,  as  determined  by  Becker,'  is  that  it  is  the  figure  of 
greatest  stability. 

Between  dome-shaped  volcanic  mountains  with  fiat 
tops,  and  conical  piles  with  a  sharp  apex  and  concave 
surfaces,  there  are  many  intermediate  forms.  These 
variations  depend  principally  on  the  alternate  extrusions 
of  projectiles  and  of  lava  from  the  same  vent,  which  leads 
to  the  building  of  compound  cones,  the  most  usual  type; 
the  location  of  the  opening  through  which  lava  escapes, 
whether  from  the  summit  or  through  the  side  of  a  crater ; 
the  degree  of  fluidity  of  the  lava,  whether  highly  liquid 
or  thick  and  viscous ;  and  the  size  and  shape  of  the  frag- 
ments thrown  out  during  expletive  eruptions. 

The  extrusion  of  highly  liquid  lavas,  as  we  have  seen, 
leads  to  the  building  of  mountains  with  very  gentle 
slopes,  as  in.  the  case  of  Mauna  Loa ;  highly  viscid  lavas, 
on  the  other  hand,  sometimes  congeal  in  nearly  perpen- 
dicular cliffs,  as  in  the  case  of  some  of  the  Mono  craters, 
California,  described  later,  but  in  such  instances  lofty 
mountains  are  not  formed,  owing  apparently  to  the  clog- 
ging of  the  conduits  through  which  the  lava  is  emitted. 

Instances  are  cited  by  Judd,^  in  which  lava  so  viscous 
that  it  refused  to  flow  on  reaching  the  surface,  has 
been  forced  out  from  volcanic  vents  and  congealed  in. 
obtuse,  steep-sided  columns,  having  a  concentric  internal 
structure.  The  form  and  structure  of  these  peculiar 
elevations  has  been  imitated  by  forcing  a  thick  paste  of 
plaster  of  paris,  vertically  upward  through  a  hole  in  a 


1 G.  F.  Becker,  "  The  Geometrical  Form  of  Volcanic  Cones  and  the  Elastic 
Limit  of  Lava,"  in  "  American  Journal  of  Science,"  3d  series,  Vol.  30,  1885, 
pp.  283-293. 

2 J.  W.  Judd,  "Volcanoes,"  pp.  125,  127. 


VOI.CAXOKS   OF  NOHTH    AMKKICA. 


I'l.ATK  n. 


Fio.  A.     Fusiyuina,  Japan.    A  typical  lapilli  cone. 


Fig.  B.    St.  Aii{;ustine,  Cook's  Inlet,  Alaska,  18',I5.     (Photograph  by  U.S.  Geological 

Survey.) 


lir 


!|f     V^-: 


>l 


n 


«||J«W1  I 


CHAUACTEUISTICS   OF    VOLCANOES 


83 


board.  In  the  experiment,  the  layers  first  formed  were 
raised  and  expanded  by  the  paste  which  followed,  so  as 
to  form  an  oval  or  bell-shaped  mass,  which,  when  cut 
through,  exhibited  an  onion-like  structure.  Examples 
of  hills  of  this  nature  are  said  to  be  furnished  by  many 
andesitic  volcanoes  in  Hungary,  certain  phonolite  hills  of 
Bohemia,  and  more  definitely  by  the  so-called  "  manie- 
lona"  of  the  Island  of  Bourbon.  Illustrations  of  the 
latter  are  given  in  the  book  just  cited. 

The  most  regular  and  by  far  the  most  Ijeautiful  cones, 
formed  of  projectiles,  are  such  as  are  built  up  by  the 
blowing  out  of  fine  dust  and  gravel-like  fragments.  The 
angle  of  repose  of  such  material  is  less  than  that  of 
rough  scoria,  and  hence  the  sides  of  the  cones  formed 
of  it  are  less  steep  than  the  slopes  of  cinder  cones. 
When  cinders  are  plastic  at  the  time  of  their  fall,  they 
fuse  together  or  adhere  one  to  another,  as  in  the  case  of 
the  driblet  cones  of  Hawaii,  and  form  the  steepest  of  all 
the  various  structures  built  about  volcanic  vents. 

Structure  of  Volcanic  Mountains 
What  arrangement  of  the  material  composing  volcanic 
mountains  would  be  revealed,  if  we  could  cut  them  from 
summit  to  base  through  a  vertical  plane  and  remove  one 
half  of  the  mass  ?  The  surface  thus  exposed  would  be  a 
vertical  section.  Although  it  is  not  possil)le  to  obtain 
complete  sections  of  this  nature  of  such  vast  accumula- 
tions, yet  volcmoes  are  sometimes  breached  by  explosions 
from  within,  and  variously  dissected  by  erosive  agencies 
acting  from  without.  By  studying  the  anatomy  of  vol- 
canic mountains  where  thus  exposed,  we  can  learn  many 
facts  concerning  their  mode  of  growth 


84 


VOLCANOES   Ol<'   NOUTII   AMERICA 


m 


Mruntains  formed  of  Lava  Sheets. — Mountains  made 
entirely  of  lava  flows  when  dissected  l)y  erosion,  reveal 
the  edges  of  the  iml)ricated  layers  of  which  they  are  com- 
posed. Those,  in  normal  instances,  dip  away  from  the 
crater  and  are  of  very  irregular  thickness.  A  sheet  may 
have  its  maximum  thickness  near  the  vertical  axis  of  the 
mountain  or  at  a  distance  from  it,  depending  on  topographic 
conditions,  the  viscosity  of  the  lava,  and  other  causes. 
The  overflows  in  the  earlier  stages  of  a  volcano's  growth 
are  connnonly  from  the  crater,  hut  as  the  mountain  be- 
comes higher,  the  force  required  to  raise  the  liquid  rock  to 
the  summit  is  increased,  and  relief  is  frequently  found 
through  fractures  in  the  crater  walls,  aided  perhaps  by  the 
melting  of  the  rock  of  which  the  mountain  is  composed. 

In  undisturbed  sedimentary  beds  the  higher  layers  in 
a  series  are  younger  than  those  below.  This  is  not  an 
invariable  rule,  however,  in  the  case  of  the  imbricated 
sheets  forming  many  volcanic  mountains,  since  an  erup- 
tion of  lava  may  escape  from  beneath  the  margin  of  an 
older  and  previously  hardened  layer.  What  have  been 
termed  "  imbricated  mountains  "  by  Powell,  in  which  the 
surface  layers  have  much  the  same  arrangement  as  the 
tiles  on  a  roof,  the  lower  layers  being  the  younger,  have 
the  structure  here  referred  to. 

The  sheets  of  lava  poured  out  in  various  ways  so  as  to 
build  up  mountain  masses,  are  not  continuous  all  about 
the  crater  from  which  they  were  extruded,  but  in  most 
instances  are  comparatively  narrow  streams  radiating 
more  or  less  definitely  from  the  centre,  which  overlap  at 
their  margins  and  may  even  cross  one  another. 

In  exceptional  instances,  as  already  stated,  lava  is 
extruded  in  an  extremely  viscous  condition,  as  is  the  case 


■■i 


CllAKACTEUlSTICS    OF    VOLCANOES 


85 


of  the  '•  inamelons "  of  the  IsUind  of  Bourbon,  and  rises 
into  obtuse  columns  and  dome-like  forms,  which  have  a 
concentric,  onion-like  structure,  when  seen  in  section. 

Cones  formed  of  Projectiles. — The  structure  of  a  vol- 
canic pile  composed  wholly  of  material  projected  into  the 
air  during  explosive  eruptions,  is  strikingly  different  from 
that  of  mountains  built  wholly  of  lava  sheets.  As  we 
have  seen,  the  topographic  form  produced  by  scoria,  lapilli, 
and  dust  falling  about  a  volcanic  vent,  is  that  of  a  cone. 


■\''-=itiI-V  .:•^l^^bVfe^■■^•riii,:•^l•■•'-•J:•.^•    *  . 


Fig.  3.  — Experimental  illustration  of  the  mode  of  formation  of  volcanic  cones  com- 
posed of  fra';mental  material.     (After  J.  W.  Jiuld.) 

The  arrangement  of  the  layers  in  a  vertical  section  of  such 
an  accumulation  may  be  illustrated  by  a  simple  experiment. 
If  a  tube  is  inserted  from  below,  in  a  hole  in  the  centre 
of  a  table,  and  sand,  sawdust,  and  other  similar  material 
is  blown  through  the  tube  by  means  of  a  bellows,  it  will 
rise  from  the  opening  and  fall  about  it  so  as  to  form  a 
conical  pile,  with  a  depression  in  its  summit.  If  black 
and  white  material  is  alternately  blown  through  the  tube, 
a  vertical  section  of  the  cone  that  is  formed  will  have  the 
structure  illustrated  in  the  above  diagram. 


86 


VOLCANOES   OF   NOllTH   AMERICA 


\. 


I  I 


1 


The  size  of  the  cone  obtained  by  such  an  experiment, 
the  steei)ne8s  of  its  sides,  etc.,  will  vary  with  the  amount 
and  character  of  the  material  used,  and  the  strength  of 
the  air  current ;  but  the  arrangement  of  the  layers  or  their 
structure,  exposed  in  a  vertical  section,  will  remain  essen- 
tially the  same.  The  layers  are  continuous  all  about  the 
orifice,  Ijut  are  inclined  in  two  directions  from  the  rim  of 
the  central  depression  or  crater.  The  pile  has  the  appear- 
ance of  being  formed  of  two  sets  of  cones,  the  smaller  set 
being  reversed  and  fitting  into  a  hollow  in  the  truncated 
summit  of  larger  series.  The  inclination  or  dip  of  the 
inner  layers  is  greater  than  that  of  the  outer  layers. 

The  arrangement  illustrated  above  has  been  found  to 
be  characteristic  of  the  structure  of  many  volcanic  moun- 
tains. In  place  of  the  mechanical  regularity  shown  in 
the  experiment,  however,  actual  lapilli  cones  commonly 
exhibit  marked  irregularities,  due  to  the  blowing  away  of 
l)ortions  of  their  walls,  and  the  subsequent  filling  of  such 
breaches,  and  to  variations  in  the  intensity  of  the  erup- 
tion which  may  admit  of  the  building  of  a  small  cone  with 
double  slopes,  within  the  crater  of  a  larger  structure. 
Some  of  the  irregularities  found  in  nature  are  shown  in 
the  following  ideal  action  of  Vesuvius. 

Variations  and  irregularities  also  occur  on  account  of 
the  effect  of  the  wind,  and  the  inclination  at  which  the 
projectiles  start  on  their  aerial  journey.  A  lapilli  cone 
in  the  region  of  the  trade  winds,  for  example,  is  usually 
found  to  be  higher  and  more  massive  on  the  leeward 
than  on  the  windw^ard  side.  But  in  spite  of  all  these 
modifying  conditions,  the  lapilli  cones  in  various  stages  of 
dilapidation  that  have  been  studied,  exhibit  in  greater  or 
less    perfection   the    characteristic    internal  structure  ob- 


I 


i.  I 


i      "t. 


CHARACTERISTICS   OP   VOLCANOES 


87 


tained  when  analogous  artificial  cones  are  formed,  as  in 
the  experiment  cited. 

Composite  Cones.  —  Although  mountains  composed  en- 
tirely of  lava  sheets,  or  made  wholly  of  projectiles,  may 
exist,  the  structures  described  as  characteristic  of  such 
mountains  are  rather  theoretical  than  illustrative  of  what 
one  liiids  when  the  study  of  actual  examples  is  under- 
taken. In  the  history  of  most  volcanoes  there  have  been 
times  when  lava  has  flowed  down  their  sides,  and  again. 


' .» 


5  Modem,  i  JUetrU  J-ofO'  i  Sccria  Bolt. 
7  InAUuig  of  Ortat  QyOtr  of  A.D.  19 

6  -Pre  Ajj&rjc  6edt  cf  Sarria  S  Lanu 
5£arly  Vauinnn  be<is,  pointfy  submanru. 
4  Ju/ht  with,  manne  thMa,  Post  FUcctnt. 

J  VoUcuiic  bedr^vUK  marui^  shells,  PostTUooviM. 
2  SandeUnej  i  MaHa  (MdagnnlEcctne, 
1  Apennjuie  Limes UrrUi  OtlOiMus. 


IS'TmagtfUxry  UnAS  ccmpUUAff  tnou/uaih> 

"When,  ai  Us  maacdjnz^m- 
MJUd^  of  Monte  Somma^ 
IXTedanveniaux^ 
nj)yhu. 
fl.OraUr 

W  Vent  of  ordinary  MruplioTU 
0.  Vent  ofJiu-ocqysmai£ruplions. 


Fig.  4.  Diagrammatic  general  section  through  Vesuvius  at  the  present  time,  showing 
the  structure,  the  substructure,  aud  the  successive  accumulations.  (After  J.  L. 
Lobley.) 

periods  when  explosions  have  occurred  and  fragmental 
material  spread  over  the  previously  formed  lava  sheets. 
Commonly,  many  such  alternations  in  the  character  of 
the  eruptions  have  occurred,  and  the  mountains  that 
result  have  a  composite  structure  —  sheets  of  lava  alter- 
nating in  an  irregular  way  with  layers  of  scoria,  bombs, 
lapilli,  and  dust. 

The  slopes  and  contours  of  composite  volcanic  moun- 
tains are  as  varied  as  is  their  internal  structure.     When 


88 


VOLCANiJliS   OF    NOUTH   AMEIIICA 


V\ 


^(l 


lava  flows  predominate  over  the  fragmental  deposits, 
their  shapes  approacli  tliat  of  the  typical  flat-topped 
domes,  of  which  Mauna  Loa  is  an  example;  when  the 
projectile  material  is  in  excess  of  the  lava  poured  out  in  a 
fluid  condition,  cones  with  small  apical  angles  and  steep, 
concave  sides,  approximating  to  the  form  of  Fusiyama, 
are  produced.     These  contrasts  are  illustrated  in  Fig.  2. 

It  is  the  fate  of  mountains,  inclusive  of  those  of  vol- 
canic origin  wliich  escape  destruction  by  explosions,  to  be 
slowly  removed  by  erosion.  During  this  process  the 
secrets  of  their  interior  are  revealed,  and  the  nature  of 
their  internal  structures  controls  the  character  of  the 
topographic  changes  they  pass  throngh. 

Dikes.  — The  structure  of  volcanic  mountains,  of  what- 
ever type,  is  subject  to  important  modifications  due  to  the 
opening  of  fissures  and  the  injection  into  them  of  molten 
rock.  Tlie  lava  filling  such  fissures  and  hardening,  forms 
sheets  wliich  may  be  vertical  or  horizontal  or  occupy  any 
intermediate  position,  and  in  fact  frequently  change  from 
one  position  to  another  that  is  quite  different,  in  the  same 
example.  Such  sheets  of  intruded  lava  which  cut  across 
the  bedding  of  the  rocks  they  invade  are  termed  dikes. 

The  fractures  formed  in  volcanic  mountains  frequently 
radiate  from  their  centres,  and  occasionally  cleave  their 
sides  from  base  to  summit.  Such  fissures  when  filled 
with  hardened  rock  add  greatly  to  the  strength  of  the 
piles  they  traverse,  and  furnish  some  of  the  most 
strongly  pronounced  topographic  features  when  volcanoes 
are  dissected  by  erosion. 

The  sheets  of  lava,  scoria,  and  lapilli  in  composite  vol- 
canic mountains  are  frequently  bound  together  by  sys- 
tems of  dikes,  which  perhaps  intersect  one  another.     The 


I 

i 


'  '"''"■UWjmp»ji 


CHAnACTEHISTICS   OF   VOLCANOES 


89 


departures  that  volcanic  mountains  coiunionly  present 
from  the  .simi)le,  ideal  type  of  lava  dt^mes  or  la})illi  cones 
depend  therefore  not  only  on  the  manner  in  Avhich  they 
arc  formed,  hut  on  suhsecpient  internal  changes.  Still 
further  complications  arise  when  the  molten  rock,  forced 
into  fissures,  reaches  the  surface  and  outflows,  forming 
surface  sheets,  and  when  explosions,  or  hasal  melting, 
remc    e  portions  of  a  mountain. 

Volcanic  Necks.  — The  passageways  or  conduits  leading 
to  volcanoes  from  deep  below  the  .surface,  and  furnishing 
a  passageway  for  the  material  erupted,  are  left  filled  with 
molten  lava  when  the  surface  activity  cea.ses ;  this  material 
slowly  cools  and  hardens  into  compact  rock,  and  forms 
what  are  termed  volcanic  necks. 

The  conduits  of  active  volcanoes  may  be  completely 
filled  with  molten  lava,  as  is  the  case  when  craters  over- 
flow. If  the  energy  declines  while  a  volcano  is  in  this 
condition,  its  crater  will  have  a  lloor  of  lava,  which  is  the 
summit  of  a  column  or  plug,  the  lower  portion  of  which, 
perhaps  miles  beneath  the  surface,  may  be  still  in  a  highly 
heated  and  plastic  condition.  At  other  times,  the  liquid 
lava  within  a  crater  and  in  the  upper  portion  of  the  con- 
duit that  leads  to  it,  may  be  drawn  off  through  fissures  in 
the  sides  of  the  volcano,  thus  causing  the  surface  of  the 
lava  column  to  fall  to  the  level  of  the  opening,  leaving  a 
more  or  less  conical  depression,  perhaps  two  or  three  thou- 
sand or  more  feet  deep.  If  the  activity  declines  while  the 
volcano  is  in  this  condition,  the  crater  will  remain  as  an 
empty  bowl  which,  especially  in  humid  climates,  may  be- 
come filled  with  water  and  transformed  into  a  lake. 

However  diverse  the  conditions  that  attend  the  growth 
of  a  volcanic  mountain,  a  core  of  lava  occupies  its  centre 


90 


VOLCANOKS   <JF    NOUTH    AMEUICA 


and  apprujiohcs  more  or  less  closely  to  its  suniiiiit.  This 
coluinn,  cooling  slowly  under  the  pressure  of  its  own 
weight,  is  changed  to  compact  rock,  which  usually  offers 
greater  resistance  to  erosion  than  the  material  with  which 
it  is  surrounded.  In  the  old  age  of  volcanic  mountains, 
wheu  their  outer  layers  are  decayed  and  washed  away, 
these  central  cores  frequently  hecome  prominent  topo- 
graphic forms.  Fine  examples  of  tower-  and  castle-like 
masses,  marking  the  sites  of  ancient  volcanoes,  occur  in 
many  parts  of  the  world.  Particular  attention  will  be 
given  in  a  succeeding  chapter  to  those  of  New  Mexico. 


i'l'  I 


^1 


V 


! 


Erosion  of  Volcanic  Mountains 

Geographers  and  geologists  recognize  two  groups  of 
forces  or  agencies,  which,  since  the  earth's  surface  was 
divided  into  land  and  water  areas,  have  struggled  with 
each  other  for  the  mastery.  One  of  these  groups  of 
forces  may  be  said  to  have  its  home  in  the  interior  of  the 
earth,  and  tends  to  modify  the  surface  of  the  globe  by 
producing  elevations  and  subsidences,  and  by  igneous 
eruptions ;  the  other  group  has  its  home  in  the  air,  and 
tends  to  modify  the  earth's  surface  in  a  variety  of  ways, 
but  principally  by  weathering  and  erosion.  The  reservoir 
of  energy  in  the  case  of  the  subterranean  forces  is  in  the 
residual  heat  of  the  earth ;  the  external  agencies  derive 
their  energy  from  the  sun. 

No  sooner  is  a  volcanic  mountain  upraised  by  subter- 
ranean forces  than  its  removal  and  the  transportation  of 
its  material  to  the  sea  is  begun.  The  destructive  work 
of  the  atmosphere  never  ceases,  although  it  may  vary 
greatly  in  intensity  from  time  to  time,  until  the  moun- 
tain, perhaps  presenting  in  its  prime  the  most  magnifi- 


i 


rii 


IBSMSmMc 


CHAUACTEIIISTICS   OF    VOLCANOES 


01 


cent  spectaclo  that  lias  ever  diversified  the  earth's  surface, 
is  cut  away  to  the  level  of  the  sea. 

The  a<^eiicies  by  which  such  stupendous  ehan<^es  are 
brought  about  are  slow  in  their  action.  Changes  of 
temperature,  by  producing  varying  stresses  in  the  rocks, 
cause  them  to  become  fractured,  especially  near  the 
surface.  Kain  falling  on  the  rocks  flows  away  as  rills 
and  brooks  which  move  the  smaller  fragments  and  by 
their  friction  cut  chamiels  in  a  mountain  side.  Water 
percolates  through  the  porous  rocks,  and  their  more  sol- 
uble minerals  are  dissolved.  While  the  mountain  is  yet 
young  this  process  of  solution  may  be  assisted  by  the 
residual  heat  of  the  rocks.  Fresh  volcanic  rocks  are 
especially  prone  to  undergo  chemical  change,  as  the  acid 
gases  that  accompany  their  extrusion  and  the  more  solu- 
ble solid  constituents  are  dissolved  by  percolating  water 
and  add  to  its  power  as  a  solvent.  When  vegetation 
takes  root  on  the  once  molten  rocks  as  they  cool,  and 
as  one  generation  of  plants  succeeds  another,  their  decay 
adds  organic  acids  to  the  water,  and  thus  still  again 
augment  their  solvent  power.  When  water  freezes  in 
the  interstices  of  the  rock,  its  expansion  acts  as  a  power- 
ful agent  in  promoting  their  disintegration. 

By  these  and  still  other  agencies,  which  for  the  most 
part  act  slowly  and  silently,  even  the  greatest  topo- 
graphic changes  resulting  from  volcanic  eruptions  are 
modified  and  finally  removed.  The  combined  action  of 
all  these  various  destructive  agencies  are  comprised  in 
what  is  termed  ivcathering  and  defjradation. 

An  interesting  feature  in  the  degradation  of  many  vol- 
canic mountains  is  seen  in  the  fact  that  the  seemingly 
weak  and   incoherent   piles  of    scoria,  lapilli,  and  dust. 


92 


VOLCANOKS   OF  NOUTII    AMKIliCA 


Ml 


I 


wliicli  fn'(iii('iitly  form  stoi-p-sidcd  coiios,  may  withstand 
tlu;  Jittauks  of  tliu  utmospliuric  agciuiii's  hotter  than  sht'uts 
of  compact  hiva,  when  exposed  to  like  conditions.  The 
secret  of  tliis  ajjparcnt  iinomaly  is  that  the  j)oroiis 
material  ahsorhs  the  water  siip[)lied  hy  rains,  and  allows 
it  to  percolate  slowly  away,  thus  ro))hin<^'  it  of  the  power 
to  erode  the  rocks  hy  (lowing  over  the  surface  and  sweep- 
ing along  fine  dehris.  The  removal  of  (h'posits  of  scoria, 
l)umice,  lai)iUi,  dust,  etc.,  is  performed  mainly  i)y  solution; 
at  least  until  the  insoluble  residue  left  behind  l)y  partial 
decay  fills  the  interstices  of  the  portion  remaining  and 
surface  streams  beconu;  possible. 

The  drainage  of  lava  sheets,  unless  fissured  and  broken 
so  as  to  allow  the  surface  waters  to  escape  downward,  is 
niaiidy  by  streams,  which,  becoming  charged  with  small 
fragments,  principally  by  the  beating  of  rain,  are  enabled 
to  carve  channels  for  them.selves.  Many  rill'*  join  to 
form  larger  lines  of  drainage ;  stream  unites  with  stream 
to  form  rivers  which  flow  away  to  the  sea.  Every  stream, 
from  the  nuisical  rill  to  the  majestic  river,  is  active  in 
deepening  its  channel  or  broadening  its  valley.  The 
steeper  the  slope,  other  conditions  being  the  same,  the 
more  rapidly  are  the  rocks  ground  away.  Monntains  are 
thus  reduced  to  hills,  plateaus  are  dissected,  and  hills  and 
plateaus  alike  are  reduced  to  plains.  Such  is  the  fate  of 
a  volcanic  mountain  although  the  march  from  topographic 
youth  to  maturity,  old  age,  and  death  may  be  modified 
and  lengthened  by  renewed  eruptions  or  elevations  pro- 
duced by  plutonic  forces. 

The  main  agencies  which  conspire  to  remove  mountains 
may  be  grouped  in  two  classes :  i.e.  mechanical  wear  and 
solution. 


U  t 


CIIARArTERISTirs   OF    VOLCANOES 


03 


.■{)- 


•la, 


llijc;ks  resist  tlinso  two  i^njups  of  aj^cucios  micqiially; 
Hoiiu'  are  hanlur  tliaii  otIici'M,  somo  aru  iiioru  soliihU'  than 
others.  For  thcso  rcasoiiH  lar^'oly,  niarkod  diversities 
appear  as  a  voleanie  luoiiiitain  is  slowly  removed.  One  of 
the  most  conspieuoMs  of  tiiese  eiian^^es,  especially  in  the 
case  of  a  mountain  composed  without  of  scoria,  lapilli,  etc., 
and  havin^^  a  core  of  solid  rock  witliin,  —  formed  hy  the 
cooling  and  harding  of  the  lava  occupyin<^  the  conduit  of 
the  volcano,  —  is  the  removal  of  the  incoherent  external 
portion,  and  the  uncovering  of  the  central  plug  or  "neck." 

Signs  of  age  in  the  case  of  a  cone  composed  of  scoria 
and  la[)iHi,  having  a  crater  at  the  summit,  are  usually 
first  made  manifest  by  the  decay  of  the  rocks  and  the 
crumbjing  of  the  crater  walls,  due  in  part  to  the  removal 
of  particles  by  the  wind,  and  the  channelling  of  the  lower 
slope  of  the  mountain  by  streams.  The  rim  of  the  crater 
at  length  disappears,  the  summit  of  the  structure  becomes 
blunted  and  forms  a  miniature  plateau  with  a  (convex 
surface,  duo  to  weathering.  As  more  and  more  of  the 
summit  is  removed,  rugged  crags  appear,  due  to  the 
uncovering  of  the  top  of  the  cohmm  of  dense  lava  within, 
or  of  portions  of  lava  streams.  The  sides  of  the  mountain 
become  more  deeply  scored  with  radiating  stream  channels. 
The  outer  sheathing  of  loose  material  is  slowly  removed, 
principally  in  suspension  and  in  solution  by  streams,  but 
in  part  by  the  wind.  As  degradation  progresses,  the 
central  core  becomes  more  and  more  prominent,  and  at 
length  stands  as  an  isolated  column,  encircled  by  a 
sloping  pediment  of  fragmental  material  —  the  wreck  of 
the  cinder  and  lapilli  cone.  In  a  more  advanced  stage 
of  waste  and  decay,  the  central  plug  increases  in  height 
in  reference  to  its  immediate  base,  as  the  surrounding 


94 


VOLCANOES   OP   NORTH   AMERICA 


I' 


% 


' 


I 


'     I. 


surface  is  lowered,  and  then  for  thousands  of  years  stands 
as  an  isolated  tower,  commemorating  the  memory  of 
the  vobano,  of  wliich  it  is  the  most  enduring  portion. 
Resistant  as  the  central  rocky  core  may  he  to  both 
mechanical  and  chemical  changes,  it  slowly  yields,  and, 
crumbling  to  dust  or  dissolved,  in  time  —  not  centu- 
ries, but  thousands  of  years  —  is  removed,  and  in  its 
place  there  is  a  plain,  perhaps  but  slightly  elevated 
above  the  sea.  One  may  walk  over  such  a  plain  without 
seeing  so  much  as  a  mound  to  represent  the  mountain, 
perhaps  snow-capped  and  glacier-crowned  in  its  maturity, 
that  was  built  by  volcanic  eruptions  ages  and  ages  before. 
The  geologist  studying  such  a  region  finds  in  the  rocks 
the  deeper  roots  of  the  vanished  mountain. 

During  the  series  of  changes  outlined  above,  especially 
in  the  case  of  a  volcanic  laountain  having  a  complex 
structure,  many  modifications  in  relief  occur,  besides 
those  mentioned.  Where  the  radiating  lava  sheets  are 
thickest,  pronounced  ridges  appear.  Dikes  are  left  in 
bold  relief  in  much  the  same  manner  as  in  the  case  of  the 
volcanic  neck.  Many  other  modifications  of  the  proy 
cess  —  dependent  both  on  internal  structure  and  composi- 
tion, and  on  external  or  climatic  conditions  —  have  been 
described  by  those  who  have  studied  the  life  histories  of 
topographic  forms,  but  enough  has  been  stated,  perhaps, 
to  interest  the  reader  in  the  ever-changing  expressions  in 
the  face  of  the  earth,  and  lead  him  to  look  for  these  feat- 
ures during  his  travels. 

Subterranean  Intrusions  of  Igneous  Rock 

Volcanoes  in  numerous  instances  have  a  linear  arrange- 
ment, and  lor  this  and  other  reasons  are  known,  in  many 


CHARACTERISTICS   OF   VOLCANOES 


95 


localities,  to  be  located  on  fissures  in  the  earth's  crust. 
Jn  fact,  there  are  many  considerations  leading  to  the  con- 
cluhion  that  the  positions  of  all  volcanoes  have  been 
determined  by  fracture  in  tlie  rocks  through  which  their 
conduits  pass.  It  is  evident,  therefore,  that  there  is  not 
only  an  intimate  but  a  genetic  connection  between  surface 
and  subterranean  igneous  phenomena.  In  discussing  this 
question  it  is  of  convenience  to  have  in  mind  a  distinction 
in  nomenclature,  commonly  recognized  by  geologists,  be- 
tween molten  magmas  that  cool  at  the  surface  and  form 
volcanic  rocks^,  and  similar  magmas  that  cool  deep  below 
the  surface  and  form  plutonic  rocks.  The  rocks  that  are 
formed  in  the  first  instance  are  ejected  or  extruded  at  the 
surface,  and  in  the  second  instance  injected  or  intruded 
among  older  rocks  below  the  surface.  To  illustrate :  a  fis- 
sure  in  the  earth's  crust  which  becomes  filled  with  molten 
rock,  usually  by  its  being  forced  in  from  below  under 
great  pressure,  may  reach  the  surface  and  give  origin  to 
a  volcano,  or  to  a  fissure  eruption ;  the  portion  of  the 
magma  that  entered  the  fissure  but  failed  to  reach  the 
surface  would  in  cooling  form  a  dike.  The  same  magma 
would  thus  form  volcanic  or  plutonic  rocks  according  to 
the  position  in  which  it  cooled. 

The  conspicuous  changes  that  volcanoes  make  at  the 
surface  attract  such  a  large  share  of  attention  on  ac- 
count of  the  vast  quantities  of  rock  extruded,  that  the 
possibility  of  an  equal  bulk  of  similar  material  being 
injected  into  fissures  and  other  openings  in  the  earth's 
crust  without  reaching  the  surface  is  apt  to  be  over- 
looked. In  connection  with  the  study  of  volcanoes  it  is 
instructive  to  have  in  mind  some  of  the  leading  facts 
concerning  these  subterranean  or  plutonic  intrusions. 


9G 


VOLCANOES   OP   NORTH   AMEKTCA 


I 


A  • 


Dikes.  —  The  formation  of  sheets  of  igneous  rock  by 
the  hardening  of  lava  in  fissures  has  already  been  men- 
tioned in  connection  with  the  structure  of  volcanic  moun- 
tains. Fractures  in  the  earth's  crust  are  not  confined  to 
the  vicinity  of  volcanoes,  however,  nor  to  the  immediate 
surface  of  the  earth.  They  are  known  to  affect  many 
regions,  no  considerable  land  areas  in  fact  being  without 
such  breaks,  and  to  cut  the  rocks  composing  the  exterior 
of  the  earth  to  a  depth,  in  man3'  instances,  of  tens  of  thou- 
sands of  feet.  The  study  of  eartliquakes  has  shown  that 
some  of  the  most  severe  shocks  have  been  caused  by  the 
formation  of  rents  in  the  rocks  several  miles  in  length 
and  at  a  depth  in  certain  instances  of  ten  or  twelve 
miles.^  All  fractures  in  the  rocks  are  not  widened  into 
fissures,  and  only  such  fissures  as  penetrate  to  reservoirs 
of  fused  rocks  or  to  regions  where  the  rocks  are  suffi- 
ciently heated  to  pass  into  a  plastic  or  liquid  condition 
when  pressure  is  relieved,  become  injected  with  molten 
magmas  so  as  to  give  origin  to  dikes. 

Igneous  dikes,"  then,  are  formed  when  fused  magmas 
are  forced  into  fissures,  and  on  cooling  and  hardening 
form  sheets  of  rock  usually  more  or  less  vertical,  which 
cut  across  the  bedding  of  the  strata  they  traverse.  They 
may  be  composed  of  any  variety  of  igneous  rock  that  is 
rendered  sufficiently  plastic  to  flow  under  great  pressure. 
It  is  probable,  especially  in  the  case  of  thin  dikes,  that 
they  are  formed  quickly,  as  otherwise  the  cooling  and 
hardening  of  the  material  first  injected  would  retard  the 
progress  of  the  advancing  sheet. 


1 


1  J.  Le  Conte,  "  Elements  of  Geology,"  4th  ed.,  New  York,  1896,  p.  138. 

2  Dikes  of  another  class  owe  their  origin  to  the  injection  of  sand  or  other 
similar  material  into  fissures. 


l"' 


CHAIIACTEUISTICS   OB'    VOLCANOES 


97 


The  rocks  adjacent  to  a  dike  are  usually  altered  in 
color  and  texture  on  account  of  the  heat  of  the  molten 
material  inje^^ted  into  them.  The  intensity  and  lateral 
extent  of  this  metamorphism  vary  according  to  the  nature 
of  the  invaded  strata,  and  the  amount  of  moisture  present. 
Many  of  the  changes  that  are  usually  included  under  the 
term  contact  metamor^jjhism,  however,  are  due  to  the 
deposition  of  mineral  matter,  most  commonly  quartz, 
from  heated  waters  that  rise  from  below  and  follow  the 
contacts  of  a  dike  with  the  adjacent  rocks.  Changes  of 
this  nature  may  continue  long  after  the  upper  portion  of 
a  dike  has  cooled ;  the  hot,  mineral-charged  water  being 
derived  from  still  highly  heated  regions  below. 

The  molten  rock  forming  dikes  cools  most  rapidly  at 
the  surfaces  of  contact  with  the  containing  rocks;  hence 
their  sides  are  frequently  much  finer  in  texture  than  the 
central  portions,  where  cooling  progresses  more  slowly  and 
larger  crystals  are  formed. 

As  in  the  case  of  lava  flows,  the  molten  rock  injected 
into  fissures  frequently  acquires  a  columnar  structure  on 
cooling,  owing  to  contraction  and  the  formation  of  joints. 
The  rock  is  then  divided  into  prisms  most  frequently  six- 
sided,  which  are  arranged  at  right  angles  to  the  cooling 
surfaces.  This  columnar  structure,  or  basaltic  structure  as 
it  is  sometimes  termed,  since  many  of  the  finest  examples 
occur  in  basalt,  is  frequently  well  marked,  and  when  the 
dikes  are  exposed  by  weathering,  gives  origin  to  striking 
peculiarities,  as  may  be  seen  from  the  accompanying 
illustration  of  a  dike,  brought  into  relief  by  the  removal 
of  the  enclosing  rocks,  that  occur  on  the  shore  of  Lake 
Superior. 

Instead  of  a  well-defined  series  of  joints   dividing   a 


H 


98 


VOU'ANOKS   OF   NOIITH    A.MIilMCA 


l{        I 


dike  into  columns,  the  rock  .sometimes  has  a  concentric 
structure  wliicli  becomes  apparent  on  weathering.  As 
decay  advances,  the  irreguhirly  jointed  material,  uniting 
the  more  compact  spherical  masses,  is  lirst  removed,  and 
houldcrs  of  (lishite(j ration  become  the  most  prominent 
features  of  the  expo.sed  edge  of  the  dike. 

The  influence  of   decayed  and  disintegrated  dikes   on 
topography  is  varied,  and  depends  on  the  chemical  and 


Fio.  5.    Columnar  dike,  shore  of  Lake  Siijierior.     (D.  D.  Owen.) 

mineralogical  nature  of  the  rock  composing  them ;  on 
their  jointed  or  concentric  structure  ;  on  the  nature  of  the 
enclosing  rock,  whether  harder  or  softer,  or  more  or  less 
soluble,  than  the  dikes  themselves ;  on  the  nature  of  the 
climate  to  which  their  outcrops  are  exposed ;  and  on  the 
nature  of  the  erosive  agencies,  whether  mainly  mechan- 
ical or  in  a  great  measure  cheruical.  etc.  At  times  dikes 
produce  prominent  rictges,  and  again  are  deeply  decayed 
and  their  material  removed  in  solution  so  as  to  give  origin 
to  depressions.     These  varying  results,  which  sometimes 


:| 


wm 


CirAUACTEUISTICS    OF    VOLCANOPIS 


99 


enter  largely  into  the  scenery  of  a  region,  cannot  be 
considered  further  at  this  tinie,  since  they  pertain  more 
strictly  to  a  study  of  the  origin  of  topographic  forms  than 
to  the  consideration  of  the  nature  of  igneous  intrusions. 

Intruded  Sheets. —  Dikes,  as  we  have  seen,  are  produced 
})y  the  injection  of  molten  rock  into  fissures.  When 
fissures  reach  the  snrface  and  lava  rises  through  tliem 
and  .flows  over  the  adjacent  country,  subaerial  or  extruded 
sheets  are  formed.  It  has  frequently  happened,  however, 
that  molten  rock  instead  of  gaining  the  surface,  has  been 
forced  in  betw^een  layers,  usually  of  sedimentary  origin,  in 
such  a  w^ay  as  to  separate  them  and  make  room  for  itself 
by  raising  the  rocks  above,  and  spread  out  so  as  to  form 
intruded  sheets. 

The  distinction  that  is  recognized  between  a  dike  and 
an  intruded  sheet,  is,  that  the  former  occupies  a  fissure 
wliich  breaks  across  the  heddbuj  of  the  enclosimj  rocks,  while 
the  latter  is  conformable  'with  the  beddinrj  of  the  adjacent 
rocks.  Probably  all  intruded  sheets,  if  traced  toward  their 
source,  would  be  found  to  pass  into  dikes.  That  is,  the 
magma  forming  an  intruded  sheet  rises  from  deep  within 
the  earth  through  fissures,  until  it  reaches  a  horizon  where 
the  rocks  are  no  longer  fractured,  and  is  then  forced  in 
between  the  strata.  If  such  a  sheet  should  meet  another 
fissure,  the  course  of  the  injected  material  might  be  again 
changed,  and,  following  the  break,  again  form  a  dike. 

The  statement  that  intruded  sheets  lie  between  strata 
of  sedimentary  rock  needs  to  be  qualified,  inasmuch  as 
intruded  sheets  might  be  formed  between  layers  of  igneous 
rock. 

Surface  lava  flows,  so  long  as  they  remain  uncovered 
by  later  deposits,  are  not  to  be   mistaken   for   intruded 


100 


VOLCANOES   OF  NOUTH   AMERICA 


IHi^ 


^1 


sheets,  although  such  an  error  might  arise  when  an 
intruded  sheet  is  revealed  by  the  removal  of  its  covering. 
When  surface  tlows  are  buried  beneath  sedimentary  layers, 
it  is  evident  that  in  a  general  way  they  would  simulate 
intruded  sheets.  A  crucial  test  by  which  the  two  may  be 
distinguished,  is,  that  an  intruded  sheet  produces  more  or 
less  metamorphism  in  the  rocks  both  above  and  below  it, 
while  an  extruded  sheet,  having  no  rocks  above  it  to  be 
altered  by  its  heat,  only  produces  a  change  in  the  subja- 
cent layers.  There  are  many  other  occurrences  which 
may  guide  one  in  determining  whether  a  layer  of  basalt, 
for  example,  exposed  in  the  sides  of  a  ravine  or  canyon, 
with  sandstone,  shales,  etc.,  both  above  and  below  it,  was 
intruded  into  its  present  position  after  the  associated  sedi- 
mentary beds  were  laid  down  and  hardened,  or  whether  it 
was  originally  a  surface  sheet,  subsequently  covered  l)y 
sediments.  Ainong  the  differences  to  be  looked  for  are 
the  structure  of  the  surface  of  the  sheet  of  basalt,  whether 
scoriaceous,  as  is  the  case  with  the  surfaces  of  lava  sheets 
that  cool  under  atmospheric  pressure,  or  compact  and 
fine  grained  like  the  sides  of  dikes  and  similar  to  both 
the  upper  and  lower  surfaces  of  intruded  sheets.  The 
presence  of  pebbles  of  basalt  in  the  ^rocks  resting  on  the 
igneous  sheet  might  also  show  that  the  superior  beds  were 
formed  after  the  igneous  reck  had  cooled.  Still  other 
indications  of  value  to  the  field  geologist  in  interpreting 
the  history  of  such  occurrences  as  just  cited,  may  be  found 
in  most  books  on  physical  geology. 

Intruded  sheets,  like  dikes,  vary  greatly  in  their 
dimensions,  and  in  the  amount  of  energy  that  they  repre- 
sent. •  At  times  their  thickness  is  to  be  measured  by  tens 
of  feet,  or  even  by  inches,  and  again  by  hundreds  of  feet ; 


,1 1 


CHARACTERISTICS    OF    VOLCANOES 


101 


an 


ate 
be 
or 
it, 
be 


tills  superficial  extent  is  sometimes  hundreds  of  square 
miles.  One  of  the  most  remarkable  instances  in  North 
America  of  the  magnitude  which  intruded  sheets  may 
attain,  is  furnished  by  the  Palisade  trap  sheet  of  New 
Jersey  and  New  York,  the  edge  of  which  forms  the  pict- 
ures(iue  Palisades  of  the  Hudson.  This  sheet  was 
intruded  into  the  sandstones  and  shales  of  the  Newark 
system,  and  has  a  diameter  from  north  to  south  of  not 
less  than  seventy  miles.  The  minimum  widtli  of  the 
portion  which  remains,  its  eastern  extension  having  been 
removed  by  erosion,  is  about  two  miles ;  its  thickness 
varies  from  oOO  or  400  at  Jersey  City,  to  850  feet  i  the 
Hook  Mountains  of  Rockland  County,  New  York.^ 

One  essential  condition  for  the  formation  of  widely 
extended  intruded  sheets  is  that  the  receiving  terrane 
shall  be  composed  of  nearly  horizontal  strata.  On 
account  of  the  weight  to  be  lifted  in  order  that  an  in- 
truded sheet  may  make  room  for  itself,  it  is  evident  that 
intrusions  of  the  nature  here  considered  are  possible  only 
in  the  upper  portion  of  the  earth's  crust.  The  absence  of 
fractures  in  the  invaded  strata  is  shown  by  the  fact  that 
the  injected  molten  rock  does  not  escape  through  fissures 
and  form  dikes  and  surface  overflows. 

Plutonic  Plugs.  —  It  is  instructive  to  notice  at  this  time 
a  class  of  topographic  features  which  have  a  striking 
resemblance  to  volcanic  necks,  but  are  of  a  different 
origin.  In  some  instances,  intrusions  of  plutonic  rock, 
instead  of  forming  dikes  or  spreading  out  in  sheets,  rise 
through   sedimentary  beds  for    some   distance  and  then. 


1  I.  C.  Russell,  "  The  Newark  System,"  U.  S.  Geological  Survey,  Bulletin 
Xo.  S'),  pp.  74-70.  X.  II.  Datton,  "  The  Relations  of  the  Traps  of  the  New- 
ark System,"  U.  S.  Geological  Survey,  Bulletin  No.  07,  pp.  37-53. 


!t 


-! 


102 


VOLCAXOKS   OF    XOUTM    AMERICA 


ll 


1  li 


I 


witlujut  t'xpiindiiig,  lift  the  (stnita  alxjve  .so  as  t(^  furni  a 
dome.  WliL'ii  erosion  remove.s  tl»e  dome  of  stratilied 
rock,  a  plug  of  igneous  rock  is  exposed  within.  These 
plug-like  nitrusious  unaccompanied  by  a  lateral  spreading 
of  the  magma,  it  is  convenient  to  designate  as  pb(to)iic 
phifjs.  Several  iiLstances  of  such  local  intrusions  into 
nearly  horizontal  sedimentary  strata  are  known  in  the 
neighljorliood  of  the  Black  Hills  of  Dakota.  On  the 
northwest  side  of  the  Black  Hills  a  remarkable  series  of 
elevations  occurs,  which  range  from  a  regular  dome  of 
stratified  beds  in  which  erosion  has  not  cut  deep  enough 
to  reveal  the  plug  below,  through  several  examples  in 
which  a  prominent  tower-like  mass  of  igneous  rock  a  few 
hundred  feet  high  rises  in  the  centre  of  concentric  ridges 
formed  by  the  truncated  edges  of  hard  layers  in  the 
base  of  a  deeply  eroded  dome,  to  a  still  more  prominent 
column  over  six  hundred  feet  high,  from  about  which  all 
remnants  of  the  stratified  rocks  that  formerly  arched  over 
it  have  been  removed.  A  description  of  these  unique 
topographic  features  and  certain  general  conclusions  tna^tc 
their  study  has  suggested,  have  been  given  elsewhere.' 

Laccolites.  —  Intermediate  in  both  form  and  size  be- 
tween intruded  sheets  and  plutonic  plugs  are  certain 
igneous  intrusions  that  after  rising  for  a  distance  through 
stratified  beds,  expand  between  the  layers  not  so  as  to 
form  widely  spread  sheets,  but  in  thick  masses  which 
raise  the  rocks  aljove  into  domes.  These  plugs  or  dikes 
with  expanded  summits  are  termed  laccolites,  or  stone 
cisterns, 

*  I.  C  Russell, "  Igneous  Intrusions  in  the  Xeighborhooil  of  tlie  IJlack  Hills 
of  Dakota,"  in  "  The  Journal  of  Geology,"  published  hy  the  University  of 
Chicago,  Vol.  4,  180(3,  pp.  23-43. 


sss. 


•  HAKACTKUISTICS    OF    V()L(JAN(»ES 


\m 


1  a 
lied 


y/Nc 


iito 


lie 


lie 


oi 


of 


Typical  exaiupk-.s  of  intrusions  of  this  cliaracter  form 
tiie  Henry  M(Hiutains  in  sontliern  Utah.  Six  or  seven 
tiioiisand  feet  of  strata  have  tiiere  been  eroded  away,  leav- 
in,^  the  hard  resistant  eores  of  tiie  former  domes  exposed. 
In  some  instances  these  cores  are  lU.OOO  feet  or  more  in 
diameter,  and  o(M)()  feet  tliiidv,  in  the  central  part.  As 
they  stand  to-day  after  a.i^es  of  decay  and  erosion,  tliey 
form  picturesque  mountains  wliicli  rank  among  the  more 
important  isohited  uplifts  of  the  United  States. 

Since  the  nature  of  laccolitic  mountains  was  lirst 
pointed  out  by  Gilbert^  many  other  occurrences  of  the 
same  nature  have  been  recognized  in  America  and  other 
countries." 

Subtuberant  Mountains.  — The  nature  and  magnitude 
of  the  injections  termed  laccolites,  i)repares  us  to  take 
still  another  step  in  unravelling  the  eompk'X  changes  pro- 
duced in  the  earth's  crust  by  molten  magmas  forced  in 
from  below. 

The  domes  formed  by  plutonic  plugs  are  in  known 
instances  from  a  mile  to  two  or  three  miles  in  diam- 
eter ;  the  domes  elevated  by  several  of  the  larger  lac- 
colites that  have  been  studied  must  have  been  from  live 
to  ten  miles  in  diameter.  Forcibly  as  these  dimensions  im- 
pre.ss  one,  they  become  of  a  secondary  order  of  magnitude 
Avlien  compared  with  similar  measurements  of  still  other 
dome-shaped  uplifts  that  occur  in  the  central  portion  of 
the  United  States. 


!! 


I! 


^  G.  K.  fJilliert,  "Report  oii  the  Geology  of  the  Henry  Mountains,"  Geo- 
graphical and  Geological  Survey  of  the  Rocky  Mountain  Region.  Washing- 
ton, D.C.,  1877. 

2  Whitman  Cross,  "The  Laccolitic  Mountain  Groups  of  Colorado.  Utah, 
and  Arizona,"  U.  S.  Geological  Survey,  14th  Annual  Report,  18"J5,  pp. 
1.J7-241. 


h 


ii. 


:  i! 

I! 


;    i 


104 


VOLrANOKS    OF    NOltTM    AMEKICA 


Tlie  Black  Hills  of  Dakota  owe  their  pn^sciit  t'onii  to 
the  sculj)tiirin«^  of  a  vast  doiiie  which  if  remodelled  woidd 
liave  a  diameter  from  northwest  to  southeast  of  IGO  miles, 
and  at  riuht  angles  to  this  direction,  of  eighty  miles,  and 
a  height  above  th(!  surrounding  plain  of  about  7000  feet. 
This  great  dome  has  been  deeply  dissected.  The  hard 
layers  in  its  basal  portion  form  concentric  rings  about  a 
central  core  of  granite.  The  dip,  or  inclination,  of  these 
upraised  i.iycr."  is  nw^ay  from  the  vertical  axis  of  the  dome 
in  all  directions.  Completely  encircling  the  outer  ring  of 
the  truncated  dome  are  horizontal  strata  for  scores  of 
miles,  of  the  same  nature  as  those  affected  by  the  uplift. 
That  is,  in  the  central  portion  of  a  vast  plain,  underlain 
by  thousands  of  feet  in  vertical  thickness  of  horizontally 
stratified  sandstones,  shales,  and  limestones,  resting  on 
metamorphosed  rocks,  there  has  been  an  uplift  produced 
by  a  force  acting  from  below  directly  upwards,  which  has 
raised  the  strata  into  a  dome  a  mile  and  a  half  in  height 
above  its  immediate  base. 

The  Big  Horn  Mountains  of  Wyoming  have  the  same 
general  structure  as  the  Black  Hills,  but  the  dome  from 
which  they  have  been  sculptured  was  much  larger.  In 
central  and  southern  Wyoming  and  in  Colorado  there 
are  still  other  uplifts  of  the  same  nature  as  those  just 
mentioned,  which  furnish  evidence  of  having  been  sculpt- 
ured from  vast  domes  that  exceed  in  size  those  that  rose 
to  form  the  Black  Hills  and  Big  Horn  Mountains. 

These  domes,  rising  as  they  do  in  a  broad  region  of 
horizontally  bedded  rock,  and  having  the  upraised  layers 
dipping  away  in  all  directions  from  a  central  region,  are 
not  of  the  nature  of  folds  produced  by  a  lateral  thrust, 
as  in  the  case  of  the  Appalachian  Mountains,  for  example, 


V 


(•lIAKACTKKIl.riCS   0|-    VdUANOKH 


M') 


to 
nld 

I  CM, 

111(1 

Ct. 

inl 
a 
se 
lie 
of 
of 

ift. 

lin 

on 

3e(l 
las 
:lit 


but  owe  tlieir  ori;^in  to  a  force  acting  from  below  u})warcls 
Tlieir  analoj^'y  in  form  and  striicturo  to  the  domes  raised 
above  pliitonic  plugs  and  laceolites  leads  to  the  inference 
that  they  owe  their  origin  to  igneous  intrusions.  Without 
restating  all  the  arguments  that  lead  to  this  eoiu^lusion, 
I  can  say  that  a  })lausil)l(»  hypothesis  in  reference  to  the 
origin  of  uplifts  of  the  type  of  the  lilack  Hills,  is.  that 
they  may  have  been  elevated  by  molten  magmas  forced 
into  the  earth's  crust,  deep  below  the  surface.  'J'he 
enlargement  of  these  deeply  seated  bodies  of  intruded 
rocks  may  be  likened  to  the  growth  of  a  tuber  in  the 
earth;  as  a  convenient  name  for  uplifts  originating  in  this 
way,  1  have  suggested  the  term  snJdahcrdnt  »notinf((ins.^ 

Generalizations. —  Tlie  srudy  of  volcanoes  and  of  sub- 
terranean intrusions  of  igneous  rock,  has  shown  that  the 
two  are  the  result  of  the  action  of  tli(»  same  series  of 
forces  and  are  in  reality  but  varying  results  of  a  single 
process.  A  proper  understanding  of  the  nature  of  vol- 
canoes cannot  be  reached  without  taking  into  consideraticju 
the  manner  in  which  injections  of  molten  matter  into  the 
earth's  crust  have  l)een  produced. 

The  nature  of  subterranean  intrusions  leads  at  once  to 
the  conclusion  that  steam  cannot  be  considered  as  the 
propelling  force  which  injected  molten  magmas  into  other 
rocks  already  cold  and  solid.  By  thus  going  t(j  the  roots 
of  the  volcanoes,  as  it  were,  the  theory  that  steam  is  the 
primary  force  which  gives  origin  to  volcanoes  is  removed. 
It  becomes  apparent  also  from  the  study  of  intrusions  that 


'! 


*  Tlie  nature  and  origin  of  subtnberant  mountains  and  tlioir  relation  to 
plutonic  plugs,  laceolites,  intruded  sheets,  and  dikes,  have  been  discussed  by 
the  writer  in  "The  Journal  of  Geology"  (Chicago),  Vol.  4,  1896,  pp. 
177-104. 


lOt; 


Vnl.CANoK.S   nr    NuUTH    A.MKKKA 


I 


iill 


.1' 


it 


tliL'  oriuiii  of  the  liL'jit  which  ciiiisi's  the  fii.siou  ol"  rocks 
(Iccj)  hclow  the  Mirfacc,  iind  the  oi'i^iu  <>♦'  tlic  jtrcs.siirt' 
wliicli  c;iii.s(!.s  tlio  inaj^iMiiM  tints  I'oriiicd  to  rise  in  (issuros 
and  lead  to  the  I'orniation  ol'  various  chisses  of  intrusions 
and  to  vol(;anoes.  are  distinct  and  should  he  separately 
considered. 

What  may  he  considered  as  a  continuation  of  the  lines 
of  thought  here  suggested,  will  he  found  in  next  t(j  the 
hist  cha[»ter  of  this  hook. 

ClIAItACTKIJISTIf'S    OI-'    IciNKUUS    RoCKS 

The  rocks  of  which  the  earth's  crust  is  conii)osed  present 
great  diversity.  In  order  to  avoid  confusion  from  the 
endless  variatiims  they  exhihit,  it  is  convenient  to  classify 
them  iirst  of  all  in  three  great  gr(ju[)s :  namely,  ujncous, 
.sediincntari/,  and  mdainorphlc,  rocks.  This  may  he  con- 
sidered the  general  order  in  which  the  rocks  were  formed 
since  the  iir.st  crust  of  the  earth,  under  the  most  plausihle 
hypothesis  that  has  heen  presented,  was  produced  hy  the 
cooling  of  fused  material.  Where  this  primal  crust  rosa. 
ahove  the  sea,  it  was  disintegrated  and  worn  away  so  as 
to  furnish  material  for  sedimentary  heds.  At  a  later  date, 
both  volcanic  and  sedimentary  rocks  were  in  many  locali- 
riis  intensely  heated  and  underwent  great  mechanical, 
chemical,  and  mineralogical  changes,  which  led  to  marked 
alterations  in  all  of  their  characteristics.  These  altered 
rocks  are  said  to  be  metamorphosed.  They  constitnte  the 
third  great  group  mentioned  above. 

In  the  restiicted  view  of  nature  presented  in  these  pages, 
we  have  but  little  to  do  with  sedimentary  and  metamor- 
pliic  rocks,  and  will  therefore  find  it  most  advantageous 
to  concentrate  our  attention  on  some  of  the  leading  char- 


■nf..."!!;: 


CMAIIACTKUISTICM    OF    VULCAXOKM 


KIT 


'I'ks 

ires 
lloiis 
L\y 

iiics 
It  lit' 


iicturistics  (jf  the  rocks  which  wen;  once  in  u  .state  of 
fusion  an<l  luivo  cooled  ami  crvstalli/cd  Iroiii  a  inoht'ii 
condition. 

An  idea  of  the  guiiLM'al  nature  of  ij^^neoiis  rock,  hut  more 
especially  of  tiiose  whieii  h;ive  I)een  thnjwn  out  hy  vol- 
canoes and  cooled  on  the  earth's  surface,  may  he  ol)tained 
hy  watching  the  slag  as  it  is  drawn  from  an  iron  furnace. 
In  order  to  ol)tain  metallic  iron,  iron  ores  are  pi.  ced  in  a 
furnace,  together,  usuall}',  with  llmestont!  and  el:  .rcoal, 
coal,  or  other  fuel.  The  comhustion  of  the  fuel  prcjduces 
suilicient  heat  to  fu.se  the  charge;,  and  chemical  changes 
lead  to  the  .separation  of  the  iron  from  the  slag.  The  slag- 
is  really  fu.sed  rock,  which  is  lighter  than  the  nujlten  iron 
and  floats  on  its  surface.  When  an  oi)ening  is  made  at 
the  proper  place  in  the  furnace,  the  slag  flows  out  as  a 
stream  of  h((uid  matter  which,  if  sutliciently  heated,  will 
run  on  a  gently  inclined  slope  almost  as  freely  as  water. 
Usually,  however,  the  slag  is  not  so  highly  heated,  and 
flows  .shiggi.shly.  Such  a  .stream  of  molten  slag  imitates 
many  of  the  phenomena  to  he  seen  when  a  volcano  dis- 
charges a  stream  of  lava.  The  slag  cools  quickly  at  the 
surface  and  forms  a  crust,  which  floats  on  tlie  still  highly 
heated  portion  below.  The  division  between  the  surface 
crust  and  the  still  Ihiid  stream  beneath  is  not  usually  well 
marked,  but  one  grades  into  the  other.  As  the  still  fluid 
portion  continues  to  flow,  the  stiffened  crust  above  is 
dragged  along  with  it  and  is  wrinkled  and  acquires  a  cor- 
rugated surface  similar  to  that  of  certain  lava  streams. 
But  little  steam  escai)es  from  the  slag  at  first,  but  in 
flowing  over  moist  sand  or  earth,  clouds  of  vapor  rise 
from  it.  An  anclvsis  of  this  steam  would  show  that 
various  gases  are  mingled  with  it.     Owing  to  the  rapid 


t"    » 


I 
I 


108 


VOLCANOES   OF   NORTH    AMERICA 


cooling  of  the  slag  some  of  the  steam  and  accompanying 
gases  are  retained  and,  expanding,  form  bubbles  which 
leave  cavities  in  the  hardening  mass.  When  the  slag  is 
of  the  proper  consistency,  it  is  so  completely  filled  with 
such  steam  cavities  as  to  be  froth-like,  and  en  coolinu: 
forms  a  substance  mucli  like  pumice.  If  we  break  a  cake 
of  slag,  we  will  usually  iind  that  the  upper  surface  con- 
tains many  more  lmbl)les,  or,  in  other  words,  is  more 
scoriaceous,  than  the  central  portion.  In  all  these  features 
an  analogy  with  the  behavior  of  a  lava  stream  will  be 
noted.  Still  further:  if  the  slag  is  allowed  to  cool  in  thin 
sheets  without  a  surface  covering,  it  will  form  a  glass-like 
material ;  if  it  cools  more  slowly,  a  stony  texture  is  pro- 
duced ;  if  covered  with  a  layer  of  dry  sand  or  earth  a  foot 
or  two  deep,  thus  confining  the  heat  and  allowing  the 
fused  mass  to  cool  still  more  slowly,  various  crystals  will 
develop.  All  the  varieties  of  slag  from  the  glassy  form 
which  has  cooled  too  quickly  for  crystals  to  apj)ear, 
tlirough  the  stony  material  in  which  crystallization  has 
been  arrested  before  well-shaped  crystals  have  formedT^ 
to  the  varieties  in  which  more  or  ^ess  well-defined  crystals 
may  be  distinguished,  may  be  duj)licated  from  a  collection 
of  the  products  of  volcanoes. 

If  we  grind  small  flakes  of  slag  and  of  the  lava  that 
most  nearly  agree  with  them  in  texture,  until  they  are 
sufficiently  thin  to  transmit  light,  we  will  find  on  examin- 
ing them  with  a  microscope  that  their  similarities,  in  many 
cases,  extend  to  their  minute  internal  structure.  A  feature 
of  special  interest,  in  such  a  comparison,  is  that  the  slag 
that  has  cooled  slowly  and  volcanic  rock  with  a  similar 
texture,  consist  of  a  glassy  base  through  v  hich  more  or 
less    perfectly   formed   crystals   of  various   minerals  are 


'S, 


CHAIIAC'TEKISTICS   OF   VOLCANOES 


100 


hich 


g   IS 


iiig 


scattered.  By  careful  selection,  a  series  may  be  obtained 
both  of  slag  and  lava,  passing  from  nearly  clear  glass  on 
one  hand,  through  varieties  hi  which  but  few  crystals  are 
enclosed,  to  more  perfectly  crystallized  material  in  which 
well-formed  crystals  exceed  in  bulk  the  glassy  base  which 
unites  them. 

Such  a  comparison  of  slag  and  lava  as  has  just  been 
suggested,  furnishes  strong  evidence  that  many  of  the 
characteristics  of  volcanic  rocks  have  resulted  from  the 
conditions  under  which  they  cooled.  By  varying  the 
composition  of  slag,  or  by  studying  the  products  of  various 
kinds  of  furnaces,  such,  for  example,  as  those  in  which 
copper,  silver,  and  other  ores  are  smelted,  it  may  be  shown 
that  some  of  the  various  physical  features  they  present 
depend  on  their  chemical  composition.  The  same  is  true, 
as  has  already  been  stated  in  speaking  of  acid  and  basic 
rocks,  of  the  lavas  extruded  by  volcanoes. 

Reverting  for  a  moment  to  the  question  of  the  ultimate 
causes  of  volcanic  eruptions,  we  recognize  the  fact  that 
the  origin  of  the  heat  in  a  furnace,  and  nature  of  the  force 
which  causes  the  slag,  etc.,  to  flow  out,  are  distinct  and 
separate.  Although  some  steam  may  escape  from  molten 
slag,  no  one  will  consider  that  it  is  the  force  of  the  im- 
prisoned vapors  and  gases  that  causes  it  to  flow.  As  I 
hope  to  make  clear  in  discussing  the  theories  that  have 
been  advanced  to  account  for  the  behavior  of  volcanoes, 
there  does  not  seem  to  be  sufficient  evidence  to  show  that 
the  steam  imprisoned  in  lava  is  the  main  or  essential 
cause  of  its  rising  in  the  conduit  of  a  volcano  and  over- 
flowing. However,  let  us  pass  this  consideration  until  we 
have  a  large  body  of  well-established  facts  in  hand,  on 
which  to  base  theoretical  deductions. 


I  I 


^1 


I     ' 


110 


VOLCANOES   OF    NOIlTH   AMERICA 


I     ^t 


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As  we  hav6  seen,  volcanic  eruptions  may  be  divided  in 
a  general  way  into  two  groups,  —  the  quiet  and  explo- 
sive. It  is  to  be  remembered,  however,  that  these  are  the 
extremes  of  a  series,  between  which  there  are  many  grada- 
tions. Let  us  see  if  these  two  types  of  eruptions  can  be 
simulated  by  the  behavior  of  the  slag  drawn  from  a 
furnace.  The  quiet  flow  of  a  stream  of  slag  when  an 
opening  is  made  at  the  riglit  time  and  at  the  proper  level 
in  a  furnace,  is  evidently  analogous  to  the  quiet  extrusion 
of  lava  from  certain  volcanoes.  If,  however,  the  molten 
slag  meets  with  a  pool  of  water,  a  steam  explosion  will 
follow.  Steam  will  be  generated  with  great  rapidity  and 
form  a  conspicuous  cloud,  and  possibly  a  sharp  explosion 
will  result  from  the  igniti'  a  i  the  gases  produced 
Fragments  of  slag  will  be  projected  into  the  air  and  fall 
on  neighboring  surfaces.  On  examining  the  fragments  of 
slag,  we  will  find  that  they  are  mostly  scoriaceous,  and  in 
some  instances  froth-like  ;  evidently  the  steam  has  found 
its  way  into  the  still  plastic  magma  and  expanded  it. 
The  lesson  suggested  by  such  an  experiment  evidently  is, 
that  if  the  lava  when  forced  up  in  the  conduit  of  a 
volcano  comes  in  contact  with  sufficient  water,  an  ex- 
plosion will  follow,  and  also  that  the  team  generated 
may  in  part  become  intimately  commimilt  J  (  r  occluded  in 
the  molten  rock.  Variations  in  the  amoii  t  <^1  water,  or 
in  the  pressure  of  the  lava  at  the  locality  where  steam  is 
formed,  the  consistency  of  the  lava,  whether  highly  liquid 
or  viscous,  etc..  will  manifestly  vary  the  results. 

A  study  of  the  Ijehavior  of  slag  suggests  a  trial  hypoth- 
esis in  reference  to  the  causes  of  the  marked  variations 
in  volcanic  eruptions.  Not  only  are  v.  e  led  to  infer  that 
tlie  source  of  heat  which  fuses  igneous  rouks,  and  the  source 


CHAllACTKUISTICS   OF   VOLCANOES 


111 


of  the  pressure  wliich  causes  the  liquid  lava  to  rise  to  the 
surface,  are  distinct,  but  that  the  steam  which  forms  such  a 
conspicuous  feature  more  especially  of  explosive  eruptions, 
has  a  different  origin  from  the  lieat  and  initial  or  primary 
pressure,  and  is  of  a  secondary  nature,  due,  we  may  say, 
to  the  accidents  that  the  rising  lavas  meet  with  on  their 
passage  to  the  surface. 

Classification  of  Igneous  Rocks  based  on  Physical  Char- 
acters.—  Rock  material  in  a  state  of  fusion,  whether 
highly  fluid  or  pasty  and  viscous,  is  termed  a  magma. 
Such  magmas  on  cooling  produce  igneous  rocks ;  this 
being  this  comprehensive  name  to  include  all  rocks  that 
have  cooled  from  a  state  of  fusion.  The  subdivision  of 
igneous  rocks  into  volcanic  and  2)^utonic,  already  referred 
to,  is  now  generally  recognized ;  the  distinction  being 
based  on  the  conditions  under  whicli  the  mao-ma  cooled. 
Molten  rock  which  reaches  the  surface  or  sufficiently  near 
the  surface  to  be  practically  relieved  of  pressure  except 
that  of  the  atmosphere,  falli?  in  the  class  of  volcanic  rocks. 
Most  of  the  solid  material  erupted  by  volcanoes  belongs 
in  this  division.'  The  molten  rock  forced  into  fissvrf^.'.  or 
forming  intruded  sheets,  laccolites,  etc.,  which  cools  below 
the  surface,  constitutes  the  great  group  of  plutonic  rocks. 
As  we  have  already  seen,  many  secondary  phenomena, 
such  as  the  scoriaceous  structure  of  volcanic  rocks,  the 
compactness  of  plutonic  rocks,  etc.,  go  with  the  conditions 
under  which  magmas  cool.  But  the  essential  distinction 
between  volcanic  and  plutonic  rocks  refers  to  the  position 
reached  by  a  magma  at  the  time  of  cooling,  and  no  defi- 


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*  The  exceptions  are  when  fragments  derived  from  the  sides  of  the  con- 
duits tin-ough  which  lava  issues  are  tlirown  out  hy  volcanoes ;  as  in  tlie  case 
of  the  limestone  blocks  found  on  the  crater  of  Vesuvius. 


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112 


VOLCANOES   OF   NORTH   AMERICA 


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nite  line  can  be  drawn  between  the  two.  The  material 
in  the  upper  portion  of  the  conduit  of  a  volcano  forms  a 
volcanic  rock,  while  material  of  the  same  character  which 
failed  to  reach  the  surface  but  cooled  under  pressure,  gives 
origin  to  a  plutonic  rock. 

The  rate  at  which  a  magma  cools  also  leads  to  well- 
marked  differences  in  the  resulting  rock.  Rapid  cooling, 
as  in  the  case  of  most  furnace  slags,  prevents  crystalliza- 
tion, and  glassy  rocks  are  produced.  The  type  of  such  a 
rock  is  the  black  volcanic  glass  known  as  obsidian.  Such 
rapid  cooling  is  seldom  possible  except  in  the  case  of 
magmas  extruded  at  the  surface,  hence  obsidian  and 
related  rocks  are  only  found  among  the  products  of 
volcanoes. 

When  a  magma  cools  less  rapidly  than  in  the  case  when 
volcanic  glass  is  produced,  minute  crystals  spring  into 
existence,  which  float  in  the  still  fused  material.  If 
solidification  takes  place  at  this  stage,  the  ground  mass 
becomes  a  glass  or  felsite,  and  scattered  through  it  are 
minute  and  more  or  less  well-defined  crystals.  Still 
slower  cooling  admits  of  a  larger  portion  of  the  magma 
becoming  crystallized,  and  in  the  great  majority  of  igneous 
rock  we  find  multitudes  of  crystals  of  various  minerals, 
united  by  a  comparatively  small  quantity  of  felsitic  mate- 
rial. As  variations  in  the  rate  of  cooling  occur  in  both 
volcanic  and  plutonic  rocks,  it  is  evident  that  in  each 
case  rocks  of  various  mineralogical  composition  may 
occur. 

A  basis  for  still  further  distinctions  in  structure  is 
found  in  the  degree  of  crystallization  that  has  taken 
place.  Rocks  in  which  only  minute  crystals  are  scattered 
through  a  felsitic  base,  are  designated  as  crijptocrystalline ; 


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CHARACTERISTICS   OB"    VOLCANOES 


113 


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when  the  crystals  are  large  enough  to  be  seen  to  some 
extent  oy  the  unaided  eye,  they  become  coarsely  crystal- 
line or  macrocrystalline.  In  many  instances  conspicuous 
crystals  from  perhaps  half  an  inch  to  one  or  two  and 
even  more  inches  in  diameter  are  developed ;  the  rock  is 
then  said  to  he  jwrjjhi/iitic,  in  reference  to  the  fact  that 
a  large  class  of  rocks  formerly  designated  as  porphyries 
had  this  characteristic. 

Classification  of  Igneous  Rocks  based  on  Chemical  Charac- 
ters.—  Igneous  rocks  also  differ  widely  among  themselves 
in  reference  to  chemical  composition,  and  attempts  have 
been  made  to  classify  them  on  this  basis.  Large  numbers 
of  chemical  analyses  have  been  made  which  show  that 
they  are  diverse  in  composition,  and  probably  contain  all 
known  elements.  These  elements  almost  always  exist 
in  combination,  the  most  common  being  silicates  of 
alumina,  magnesia,  lime,  potash,  and  soda,  frequently 
with  the  addition  of  magnetic  iron  and  phosphate  of  lime. 
On  classifying  many  analyses  of  igneous  rocks,  it  becomes 
apparent  that  they  fall  in  two  somewhat  well-defined 
groups,  in  reference  to  the  amount  of  silica  they  contain. 
In  one  group  the  silica  present,  considered  as  an  acid, 
has  been  sufficient  to  satisfy  all  the  bases ;  in  the  other 
group  the  silica  is  in  excess.  On  this  plan  of  classifica- 
tion, as  has  already  been  stated,  the  rocks  containing 
sixty-six  per  cent  or  more  of  silica  are  termed  acid  rocks; 
and  those  containing  about  fifty-five  per  cent  or  less  are 
designated  basic  rocks. 

The  acid  rocks,  on  account  principally  of  the  preponder- 
ance of  highly  silicated  feldspar  present,  are  usually  light 
colored ;  while  basic  rocks,  principally  on  account  of  the 
abundance  of  iron-bearins  minerals,  are  dark  rocks.     The 


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114 


VOLCANOES  OF  NORTH  AMERICA 


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specific  gravity  of  acid  rocks  in  general  is  less  than  that 
of  basic  rocks ;  the  specific  gravity  of  the  former,  as  a 
rule,  ranging  from  2.3  to  2.7,  and  the  latter  from  2.7 
to  3.1. 

With  only  a  few  analyses  of  igneous  rocks  at  hand,  it 
might  be  found  that  their  classification  into  acid  and 
basic  would  be  somewhat  sharply  defined.  With  a  large 
number  of  analyses  available,  however,  especially  of  rocks 
from  numerous  localities,  it  will  usually  be  found  that 
a  selection  can  be  made  which  will  show  a  somewhat 
complete  gradation  from  typically  acid  to  typically  basic 
examples.  To  meet  this  difficulty  an  intermediate  group, 
to  include  such  rocks  as  are  not  decidedly  acid  or  basic, 
has  been  proposed.  Ultra-acid  rocks  are  such  as  contain 
a  high  percentage  of  free  quartz. 

The  classification  of  rocks  on  a  chemical  basis,  as  just 
described,  is  not  confined  to  those  of  igneous  origin,  but 
may  be  made  to  include  metamorphic  and  even  sediment- 
ary rocks  as  well. 

Characteristic  examples  of  acid  rocks  are  furnished  by 
granite  and  the  light-colored  igneous  rocks,  known  as 
rhyolite,  trachyte,  etc.  Ordinary  obsidian  and  pumice  also 
fall  in  this  group.  The  basic  rocks  are  typically  repre- 
sented by  basalt,  and  allied  rocks  which  are  character- 
istically dark  and  heavy.  The  rocks  mentioned  in  this 
paragraph  are  briefly  described  a  few  pages  in  advance. 

Classification  based  on  Mineralogical  Characters.  —  The 
slow  cooling  of  a  magma,  as  we  have  seen,  is  accompanied 
by  the  crystallization  of  the  substances  it  contains.  If 
the  cooling  is  rapid,  a  crystalline  glass  is  produced,  but  not 
well-defined  individual  crystals.  The  slower  the  cooling, 
the  greater  the  opportunity  for  the  molecules  of  various 


CHARACTERISTICS   OF   VOLCANOES 


115 


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substances  to  arrange  themselves  in  the  definite  forms 
we  term  crystals.  While  the  size  of  the  minerals  thus 
formed  is  regulated  mainly  by  die  rate  of  cooling,  their 
composition  depends  on  the  elements  present  in  the  magma 
and  on  their  relative  proportions  and  on  other  conditions. 
Hence  the  minerals  composing  igneous  rocks  may  be 
taken  as  a  basis  for  their  classification. 

In  porphyritic  and  macrocrystalline  rocks,  the  miner- 
alogical  composition  can  frequently  be  determined  by  the 
unaided  eye,  or  by  the  use  of  a  simple  magnifying  glass, 
but  a  more  satisfactory  method  and  one  indispensable  in 
the  examination  of  cryptocrystalline  and  glassy  rocks, 
is  by  means  of  a  microscope.  For  this  purpose  thin  flakes 
are  struck  off  from  a  rock  with  a  hammer,  or  obtained 
by  sawing  it  into  thin  sheets  by  means  of  a  revolving 
metal  disk  charged  on  the  edge  with  an  abrading  sub- 
stance like  diamond  dust.  These  flakes  are  then  ground, 
usually  with  emery,  until  sufficiently  thin  to  transmit 
light,  and  mounted  in  Canada  balsam  on  a  strip  of  glass.' 

"When  thin  sections  of  igneous  rocks  aro  examined  under 
a  microscope,  a  low  power  being  usually  the  most  satis- 
factory, it  will  be  seen  that  in  the  majority  of  instances 
they  are  composed  of  crystals  of  various  minerals  em- 
bedded in  a  glassy  or  cryptocrystalline  base  or  ground 
mass.  Of  all  but  the  most  minute  crystals,  only  sections 
are  seen ;   that  is,  the  pellicles  of  rock  are  so  thin  that 

1  Instructions  for  preparing  rock  sections  for  microscopical  examination, 
as  well  as  descriptions  of  the  optical  properties  of  i.iinerals,  the  character- 
istics and  classification  of  rocks,  etc.,  are  given  in  mn.ny  books  on  petrology. 
Among  those  usually  most  accessible  are :  Frank  llutley,  "  The  Study  of 
Rocks,"  New  York,  1879.  J.  W.  Judd,  "Volcanoes,"  New  York,  1881,  pp. 
59-66.  H.  Rosenbusch,  'Microscopical  Petrography,"  translated  by  J.  P. 
Iddings,  New  York,  1889.  E.  H.  Williams,  "  Manual  of  Lithology,"  New 
York,  1895.    J.  F.  Kemp,  «'  A  Handbook  of  Rocks,"  New  York,  1896. 


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116 


VOLCANOES   OF    NOUTH    AMERICA 


only  slices  cut  from  the  various  minerals  contained  in 
them  are  obtained.  The  slices  of  crystals  reveal  various 
outlines  according  to  the  direction  in  which  they  are  cut. 
The  identity  of  the  minerals  is  determined  in  part  from 
the  sliapes  of  these  cross-sections  A  section  of  a  quartz 
crystal,  for  example,  cut  at  right  angles  to  its  longer 
axis,  will  reveal  a  hexagonal  figure ;  a  cube  of  iron  pyrite 
will  give  a  rectangle,  if  cut  parallel  to  any  axis,  etc. 
Combined  with  a  petrographic  microscope  is  a  polariscope. 
As  minerals  transmit  light  in  accordance  with  the  arrange- 
ment of  their  molecules,  the  crystallographic  systems  to 
which  they  belong  may  in  most  instances  be  determined 
by  the  changes  they  produce  in  polarized  light. 

It  is  impossible  in  the  space  at  command,  to  give  any- 
thing like  an  adequate  outline  of  the  methods  used  in 
determining  the  minerals  of  which  rocks  are  composed  by 
the  modern  petrographic  methods,  or  of  indicating  the 
schemes  for  classifying  rocks  based  on  such  studies.  I 
wish  to  say,  however,  that  the  student  who  uses  the 
microscope  in  connection  with  the  field  study  of  rocks,  has 
a  most  interesting  and  really  faschiating  path  of  inquiry 
open  before  him.  The  beauty  of  many  of  our  most  com- 
mon rocks  when  ground  sufficiently  thin  to  transmit 
light,  and  examined  by  means  of  polarized  light,  is  truly 
surprising.  The  colors  that  blaze  forth  when  sections  of 
feldspar  and  many  other  common  minerals  are  examined 
in  this  way,  and  the  changes  of  color  produced  when  the 
polarizer  is  revolved,  are  beautiful  beyond  all  conception. 
The  most  gorgeous  harlequin  opal  becomes  pale  and 
lustreless  in  comparison  with  the  rainbow  tints  seen  in 
the  light  that  has  passed  through  a  section  of  a  wayside 
pebble.     The   microscope   not    only  reveals    the    minute 


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CHAHACTEIUSTICS   OF    VOLCANOES 


117 


organisms  of  a  foniiorly  unseen  world,  but  lias  made  the 
very  stones  write  their  histories  in  characters  of  light. 
Nor  are  these  gorgeous  displays  mere  play  to  fascinate 
the  eye.  Some  of  the  most  profound  i)r()l)lems  that  the 
geologist  meets  with  in  reference  to  the  origin  of  rocks, 
and  the  many  changes  they  have  undergone,  have  been 
successfully  attacked  by  this  modern  method  of  detailed 
and  painstaking  study.  Field  explorations  during  which 
the  character  and  relation  of  great  bodies  of  rock  are 
investigated,  should  be  followed  by  laboratory  study  of 
selected  samples,  embracing  chemical  analyses,  microscon- 
ical  investigation,  etc.  This  combination  of  the  study  of 
rocks  as  they  occur  in  the  crust  of  the  earth  and  their 
more  special  characteristics  as  revealed  in  the  laboratory, 
is  termed  jyetrologij. 

The  classification  of  rocks  based  on  their  mineralogical 
composition,  is  too  extended  and  too  technical  a  sul)ject  to 
be  introduced  at  this  time.  Some  few  facts  concerning 
this  branch  of  geology,  however,  and  a  brief  description  of 
some  of  the  more  common  igneous  rocks,  will  assist  the 
student  in  reading  the  account  of  the  volcanoes  of  North 
America  which  follows  this  introductory  chapter. 

A  classification  based  on  the  microscopical  structure  of 
igneous  rocks  adopted  by  certain  petrographers,  recognizes 
three  leading  types  of  micro-structure  ;  namely,  fjranular, 
porphyritlc,  and  glassy.  Other  students  claim  that  two 
stages  of  crystallization  may  usually  be  recognized,  the 
first  characterized  by  the  growth  of  large  crystals  in  a 
still  molten  magma,  and  the  second  by  the  formation  of 
much  smaller  crystals  which  are  arranged  about  the  mem- 
bers of  the  older  series.  In  some  rocks  the  former,  and 
in  other  rocks  the  latter,  of  these  two  phases  of  crystal- 


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VOLCANOES  OP  NORTH   AMEItlCA 


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lization  predominates.  Two  leading  classes  of  rocks  are 
thus  recognized :  1st,  the  holo-crystaU'uic  or  granitoid 
rocks,  the  type  being  granite,  composed  of  crystals  belong- 
ing to  a  8inj^le_  epoch  of  crystallizatign,  but  in  which 
neither  an  amorphous  ground  mass,  nor  crystallites  (small, 
undeveloped  crystals)  are  present ;  2d,  the  semi-crystal- 
line or  trashjtoid  rocks  (the  type  being  trachyte),  dis- 
tinguished Ijy  a  more  marked  contrast  between  the 
crystals  of  the  first  and  second  periods  of  consolidation, 
and  the  presence  usually  of  an  amorphous  ground  mass  in 
which  the  crystals  are  embedded.  To  these  a  third  and 
subordinate  class  is  sometimes  added  lo  include  such 
rocks  as  are  composed  wholly  of  glass,  without  emljedded 
crystals. 

Under  each  of  these  family  groups  several  genera,  as 
they  may  be  termed,  and  numerous  species  have  been 
recognized.  A  few  of  the  most  common  genera  are 
noticed  below.  The  first,  granite,  will  serve  as  a  repre- 
sentative of  the  great  class  of  wholly  crystalline  rocks  to 
which  it  has  given  a  name ;  while  the  others,  basalt, 
rhyolite,  trachyte,  and  andesite,  will  stand  for  the  equally 
great,  and  yet  more  diversified,  class  of  semi-crystalline 
rocks. 

Granite. —  The  great  diversity  in  color  and  texture  of 
the  rocks  of  this  type  is  probably  familiar  to  the  reader 
from  the  many  varieties  used  for  monumental  and  archi- 
tectural purposes.  Its  color  varies  through  many  grada- 
tions from  dark  gray  or  nearly  black,  to  pink  and  red, 
according  to  the  predominant  mineral  constituent.  The 
minerals  composing  granite  are  quartz,  feldspar,  and  mica, 
but  many  times  accessory  minerals  occur  in  abundance. 
The  quartz  is  readily  recognized  from  its  resemblance  to 


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CHARACTEUISTICS   OF    V(JLCANOES 


119 


clear  glass,  its  liardness  (it  will  scratch  glass),  and  the  fact 
that  it  is  without  cleavage;  that  is,  it  will  hreak  in  one 
direction  as  readily  as  in  any  other,  the  surfaces  of  fracture 
being  uneven.  The  feldspar  varies  from  white  to  pink  in 
color,  and  cleaves  easily  along  certain  parallel  planes,  pro- 
ducing smooth  brilliant  surfaces.  It  is  softer  than  ([uartz, 
can  be  scratched  with  a  knife,  but  will  not  scratch  glass. 
The  mica  splits  easily  into  thin  plates  or  scales,  which  arc 
ela.stic.  It  is  softer  than  the  feldspar,  and  frequently 
dark  in  color  and  even  black. 

If  one  examines  a  piece  of  polished  granite  either 
with  a  pocket  lens  or  a  microscope,  it  will  be  found  that 
with  the  possible  exception  of  certain  accessory  minerals, 
it  is  composed  of  more  or  less  perfect  crystals  of  the 
three  minerals  described  above,  which  interlock  with  one 
another  in  almost  all  instances  without  an  intervening 
glassy  or  micro-crystalline  ground  mass ;  that  is,  all  of  the 
substance  present  has  been  crystallized  —  the  rock  is  liolo- 
crystalline.  Recent  studies  have  shown,  however,  that 
while  nothing  like  a  vitreous  ground  mass  can  be  dis- 
covered, certain  granites  do  contain  a  minutely  crystalline 
ground  mass,  in  which  the  larger  crystals  are  embedded. 
This  illustrates  the  fact  that  even  the  larger  groups  into 
which  rocks  are  divided  are  really  artificial ;  in  reality, 
there  is  no  sharp  division  between  holo-  and  semi- 
crystalline  rocks.  Their  crystalline  condition  depends 
largely  on  the  rate  at  which  they  cool.  Between  those 
which  cool  so  slowly  that  all  the  material  present  passes 
to  a  crystalline  condition,  and  those  which  cool  more 
rapidly,  but  yet  harden  before  all  of  the  material  present 
has  assumed  definite  crystalline  forms,  there  must  of 
necessity  be  a  complete  gradation. 


ja^titoirffi^^aa***^^^ 


:^V,^..-^.^^..-;.t..-^-.^^   .■^..■wt>-,»>it.,^,.  .,       - 


120 


VOLCANOES   or   NORTH    AMKKICA 


I'  •' 


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Ik  It  I 


I  I 


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While  granito  docs  not  occur  in  the  contUtion  of  a 
surface  (low  and  is  not  known  to  have  been  produced  by 
volcanouH,  it  i.s  found  abundantly  as  bosses  and  dikes  and 
forming  vast  masses  which  were  intruded  in  a  molten  or 
plastic  condition  among  other  rocks,  and  now  exposed  by 
deep  erosion.  It  also  occurs  as  the  surface  rock  over 
vast  areas,  where,  again,  great  erosion  has  taken  place. 
In  such  instances  it  is  sometimes  found  to  pass  on  its 
border  into  gneiss  and  schist  and  other  rocks  that  are 
termed  nietamorphic ;  that  is,  it  passes  by  insensible 
gradations  into  rocks  usually  of  sedimentary  origin,  that 
have  been  changed  by  pressure,  heat,  and  the  passage 
through  them  of  heated  waters,  into  a  crystalline  condi- 
tion. These  nietamorphic  beds,  again,  when  examined  at 
a  distance  from  the  granite,  aro  sometimes  found  to  pass 
by  insensible  gradations  into  hiary  sedimentary  strata 
like  shale,  limestone,  etc.  In  such  instances  it  is  plain 
that  the  gneiss  and  schist  have  been  formed  by  the  altera- 
tion of  sedimentary  beds,  and  the  inference  is  that  the 
granite  is  but  another  step  in  the  same  process. 

Granite  also  occurs  in  the  axes  of  many  mountain 
ranges,  where  elevation  and  deep  erosion  have  taken 
place.  Occasionally  the  side  of  a  fracture  in  the  earth's 
crust  has  been  upraised,  perhaps  many  thousands  of  feet, 
so  as  to  expose  granite  as  the  basal  member  of  a  great 
series  of  rocks.  It  appears,  therefore,  that  granite  may 
be  either  an  igneous  or  a  metamorphic  rock.  Igneous, 
when  it  has  been  in  a  state  of  fusion  and  allowed  to  slowly 
crystallize ;  and  metamorphic  when  the  original  material 
changed  to  a  crystalline  form  without  complete  fusion. 
Between  the  two  processes  there  is  a  complete  gradation, 
and  no  one  can  say  where  the  boundary  line  should  be 


CIIAUACTEKI8TICS   OK    VULCAN(JES 


121 


drawn.  To  wliu^li  class  a  samplo  of  granite  belongs  can 
only  be  dctcnnincd  by  litdd  study,  and  even  then  a  definite 
answer  cannot  always  be  obtained. 

Granite  as  a  rule  deconiijoses  wben  exposed  to  tlie 
act'on  of  tlie  atniospbcre,  witb  coniiiarative  ease.  Tlie 
feldspar  yields  to  solution.  The  ([uartz  is  broken  by 
changes  of  temperature,  etc. ;  the  mica  separates  into 
flakes  and  scales.  These  surface  (;hanges  f  recjuently  extend 
to  a  depth  of  one  or  two  hundred  feet.  When  the  de- 
cayed rock  is  within  the  reach  of  streams,  it  is  washed 
away  and  its  various  ingredients  assorted,  and  in  many 
cases  deposited  separately.  The  decomposed  feldspar 
forms  clay,  some  of  which  is  pure  white  and  known  as 
kaolin  or  china  clay  ;  the  quartz  forms  sand,  in  which 
si)angles  of  mica  commonly  occur. 

Basalt. — Next  after  granite  and  allied  rocks,  the  most 
abundant  crystalline  rock  that  the  student  of  the  earth's 
history  is  apt  to  meet,  is  basalt  and  its  near  relatives. 
Familiar  examples  of  the  occurrence  of  basaltic  rocks  are 
furnished  by  the  Palisades  of  the  Hudson  ;  Blomidon  and 
North  Mountain,  Nova  Scotia ;  Mts.  Holyoke  and  Tom, 
Massachusetts ;  the  Columbia  lava  of  Oregon,  Washington, 
and  adjacent  states  ;  the  products  of  the  Hawaiian  volca- 
noes ;  the  columnar  rocks  of  the  Isle  of  Staffa,  Scotland, 
and  the  Giant's  Causeway,  Ireland,  and  at  many  other 
localities. 

Ba.salt  is  normally  a  dark,  heavy  rock,  varying  in  com- 
pactness from  scoria  filled  with  steam  cavities,  to  a  dense 
material  without  visible  apertures.  It  varies,  also,  in 
texture  from  coarsely  crystalline,  when  distinct  crystals 
are  visible  to  the  naked  eye,  to  cryptocrystalline,  and  in 
some  instances  is  a   compact   black   glass  with   perhaps 


122 


VOLCANOES   OF   NORTH   AMERICA 


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minutej  immature  crystals.  The  minerals  composing  it 
are  essentially  feldspar,  augite,  and  magnetite.  The  feld- 
spar is  most  abundant,  and  is  usually  the  species  known 
as  lahradorite,  which,  like  nearlv  all  of  the  group  to  which 
it  belongs,  is  essentially  a  silicate  of  alumina,  but  is  com- 
paratively poor  in  silica.  Other  and  more  highly  silicated 
feldspars,  however,  may  take  the  place  of  the  labradorite 
or  be  associated  with  it.  The  light-colored  crystals  to  be 
seen  in  coarse-grained  basalts  are  feldspar ;  sometimes  two 
varieties  may  be  distinguished  by  the  unaided  eye.  The 
augite  and  magnetite  are  dark  minerals,  the  magnetite 
being  always  black,  and  give  to  the  rock  much  of  its 
sombre  tone.  With  these  more  essential  minerals,  others, 
such  as  olivine,  leucite,  mica,  garnets,  etc.,  may  be  de- 
veloped as  accessories. 

Labradorite  is  the  most  easily  fusible  of  the  feldspars; 
augite  and  magnetite  are  also  easily  fusible,  so  that  basalt 
melus  at  a  comparatively  low  temperature.  Between  2000 
and  2400  degrees  of  the  Fahrenheit  scale  under  ordinary 
atmospheric  pressure  it  becomes  fluid. 

Basalt  forms  by  far  the  larger  part  of  the  lava  poured 
out  by  modern  volcanoes,  and  occurs  also  in  many  dikes 
and  in  both  extruded  and  intruded  sheets.  It  is  the  most 
common  of  all  the  recks  with  which  the  student  of  vol- 
canoes has  to  deal. 

Rhyolite  (known  also  as  liparite  and  quartz-trachyte) 
is  composed  of  a  fine-grained  ground  mass  with  crystals 
or  crystalline  kernels  of  sanidine  (a  glass-like  feldspar), 
quartz,  black  mica,  and  hornblende,  and  a  considerable 
vari3ty  of  less  abundant  minerals  scattered  through  it. 
While  considerable  diversity  is  exhibited  in  its  texture,  it 
may  usually  be  recognized,  or  at  least  have  its  identity 


CHARACTERISTICS  OF  VOLCANOES 


123 


suggested,  by  a  certain  flow-like  arrangement  of  the  min- 
erals of  which  it  is  largely  composed.  In  most  instances 
it  is  apparent  that  the  magma  was  fluid  after  the  larger 
crystals  had  been  developed  in  it  and  that  a  flowing 
motion  caused  the  crystals  to  be  arranged  with  their 
longer  axes  in  parallel  directions.  This  flow  structure 
and  the  presence  of  prominent  crystals  of  sanidine  and 
quartz  are  the  characteristic  features  that  catch  the  eye 
in  rough  field  examinations. 

Rhyolite  varies  in  color  from  black  and  dull  gray  to 
light  pink  and  even  pure  white,  and  also  exhibits  all 
degrees  of  texture  from  light,  porous  pumice  to  compact 
glass.  It  is  a  common  product  of  volcanic  eruptions, 
although  occurring  in  connection  with  but  few  still  active 
volcanoes.  It  was  poured  out  abundantly  in  compara- 
tively recent  geological  times  in  the  western  part  of  the 
United  States,  and  forms  large  portions  of  the  mountains 
of  Utah  and  Nevada.  Its  brilliant  colors  frequently  give 
to  the  mountains  of  that  arid  and  but  scantily  plant- 
clothed  region,  as  rich  and  varied  tints  as  are  seen  on  the 
hills  of  New  England  in  autumn. 

Rocks  composed  of  angular  fragments  of  rhyolite, 
cemented  so  as  to  form  a  light,  porous  mass,  termed 
rhyolitic  tuff,  occupies  large  areas  in  the  Cordilleran 
region,  and  frequently  surpasses  the  outcrops  of  massive 
rhyolite  in  brilliancy  and  variety  of  color.  The  Sunset 
Hills,  Nevada,  have  been  so  named  in  reference  to  the 
varied  color  imparted  to  them  by  the  tuff  of  which  they 
are  largely  composed.  Some  of  these  tuff  deposits  are 
direct  accumulations  of  lapilli,  blown  out  of  volcanoes 
in  a  state  of  violent  eruption;  while  other  deposits, 
frequently  of  great  extent,  are  of  the  nature  of   mud 


•  ■-^.^..^^-.•.■.. 


124 


VOLCANOES   OF  NORTH   AMERICA 


%i 


1. 1 


flows,  the  ejected  fragments  having  been  mixed  with 
water  so  as  to  render  the  mass  plastic,  and  allow  it  to 
flow  even  on  gentle  slopes. 

The  rhyolites  are  acid  rocks,  and  among  the  most 
difficultly  fusible  of  any  of  the  volcanic  series.  Analyses 
of  fifteen  samples  from  widely  separated  localities,  com- 
piled by  J.  F.  Kemp,  show  from  63.63  to  83.59  per  cent 
of  silica. 

Trach3rte.  —  This  name  was  originally  applied  to  a 
large  group  of  rocks,  characterized  principally  by  their 
roughness  and  harshness  to  the  touch,  to  which  the  name 
refers,  but  is  now  restricted  to  certain  compact,  porphy- 
ritic  material,  containing,  as  essential  ingredients,  sanidine 
with  some  other  feldspar,  and  usually  hornblende,  biotite 
(black  mica),  magnetite,  and  other  less  common  minerals, 
scattered  through  a  glassy  or  finely  crystalline  ground 
mass. 

Trachyte  is  distinguishable  from  rhyolite  by  the  ab- 
sence of  quartz  in  conspicuous  grains  or  crystals,  and  also 
by  the  absence  of  a  flow  structure.  It  is  normally  dark 
colored,  but  seldom  has  the  black  or  greenish-bladk  color 
of  basalt,  and  differs  from  that  rock  also  in  containing 
sanidine,  and  being  without  grains  or  crystals  of  olivine. 
The  trachytes  are  less  acid  than  the  rhyolites,  the  silica 
varying,  ordinarily,  from  57  to  66  per  cent. 

Andssite.  —  The  rocks  of  this  widely  distributed  group 
were  first  studied  in  the  Andes,  whence  the  name,  and 
are  described  by  E.  H.  Williams,  as  generally  dark,  and 
mostly  fine-grained  rocks,  with  a  restricted  amount  of 
glassy  base,  but  larger  than  in  the  trachytes.  When 
examined  under  the  microscope,  they  reveal  a  felt-like 
mass  of  minute  crystals  of  plagioclase,  hornblende  biotite, 


w 


CHARACTERISTICS   OF    VOLCANOES 


125 


V 


and  pyroxene,  and  may  or  may  not  contain  quartz.  In 
hornblende-andesite,  crystals  of  plagioclase,  hornblende 
in  large  black  prisms  and  needles,  and  some  augite  may 
be  distinguished  by  the  unaided  eye.  In  mica-andesite, 
biotite  predominates  over  the  hornblende. 

The  variety  characterized  b}^  the  presence  of  large-sized 
crystals  of  hornblende  is  common  in  the  Cordilleras  from 
Central  America  to  Alaska,  and  in  the  prevalent  rock 
met  with  in  many  of  the  great  volcanic  mountains  of 
which  Mt.  Rainier  and  Mt.  Shasta  are  representative. 

The  andesites  contain  from  56  to  67  per  cent  of  silica, 
corresponding  in  this  respect  very  closely  with  the 
trachytes. 

Summary.  — Under  each  of  the  typical  and  character- 
istic igneous  rocks  mentioned  above,  there  are  many 
subdivisions,  and  besides,  there  is  a  host  of  rock  species, 
some  of  them  common  in  many  districts,  that  cannot  be 
classed  in  the  group  to  which  attention  has  been  directed. 
To  attempt  a  more  extended  introduction  to  the  study  of 
rocks,  however,  is  impracticable  at  this  time ;  one  reason 
being  that  the  subject  is  so  attractive  that  the  reader 
would  be  in  danger  of  losing  sight  of  the  main  object  of 
this  book.  Petrology  is  a  highly  specialized  branch  of 
geology,  and  one  concerning  which  the  general  student 
cannot  hope  to  obtain  more  than  an  unsatisfactory  in- 
sight. Unfortunately,  there  is  no  ready  way  in  which 
the  species  of  fine-grained  igneous  rock  can  be  certainly 
distinguished  one  from  another,  without  the  use  of  some- 
what expensive  apparatus.  Thin  sections  have  to  be 
ground  and  examined  with  a  microscope  adapted  to  the 
purpose,  before  their  mineralogical  composition  can  be 
determined,  and  oven  then,  owing  to  the  great  number 


mM 


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126 


VOLCANOES  OF  NORTH  AMERICA 


of  varieties  that  occur  and  their  gradations  one  into  an- 
other, and  the  alterations  that  have  taken  place  in  numer- 
ous instances  since  the  original  cooling  of  the  magma, 
no  entirely  satisfactory  scheme  of  classification  seems 
possible.  The  best  that  the  beginner  can  do  is  to  become 
acquainted  with  a  few  types  of  the  most  common  occur- 
rence. A  few  books  have  been  mentioned  in  a  preceding 
foot-note  for  the  benefit  of  the  student  who  may  wish  to 
learn  more  of  the  science  of  petrology. 


y, 


I 


CHAPTER  II 

GENERAL   DISTRIBUTION  OF    THE  ACTIVE  AND  RECENTLY 
EXTINCT  VOLCANOES  OF  NORTH  AMERICA 

On  the  accompanying  map,  Plate  1,  the  distribution 
of  the  active  and  recently  extinct  volcanoes  of  the  world 
is  shown  with  as  much  accuracy  as  the  scale  of  the  map 
will  allow.  The  most  prominent  fact  brought  out  by 
a  study  of  the  geographical  distribution  of  volcanoes  is, 
that,  with  but  few  exceptions,  they  are  situated  on  the 
borders  of  continents  or  on  the  ocean's  floor,  and  are 
notably  absent  from  the  central  portions  of  continental 
areas. 

An  inspection  of  the  map  just  referred  to,  will  show 
that  the  volcanoes  of  North  America  form  a  part  of  a 
great  system  of  volcanic  vents  which  may  be  said  to  sur- 
round the  Pacific  Ocean.  This  chain  of  fire,  as  it  has 
been  termed,  beginning  in  Terra  del  Fuego,  extends  along 
the  west  border  of  South  America,  where  its  course  is 
marked  in  the  Andes  by  some  of  the  loftiest  igneous 
mountains  in  the  world ;  it  is  narrow  and  well  defined  on 
the  west  border  of  Central  America  and  far  into  Mexico, 
where  still  steaming  craters,  some  of  which  are  among 
the  highest  summits  on  the  continent  of  North  America, 
define  its  position.  The  volcanic  belt  broadens  in  the 
northern  part  of  Mexico  and  the  United  States,  but  is 
unmarked  by  active  craters.  Again  contracting  and 
approaching  close  to  the  ocean's  shore,  and  in  several 

127 


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128 


VOLCANOES   OF   NORTH   AMERICA 


instances  marked  by  island  volcanoes,  the  igneous  belt 
follows  the  coast  of  British  Columbia  and  Alaska,  and 
extends  westward  throughout  the  length  of  the  Aleutian 
islands.  Still  active  craters  in  Alaska  show  the  positions 
of  earth  fractures  which  unite  the  volcanic  belt  of  the 
New  World  with  the  still  more  energetic  volcanoes  of 
Kamchatka,  Corea,  Japan,  Formosa,  the  Philippine  islands. 
New  Guinea,  New  Hebrides,  New  Caledonia,  and  New 
Zealand.  The  length  of  this  vast  system  of  active  vol- 
canoes, from  the  southern  end  of  South  America  about 
the  northern  Pacific  to  New  Zealand,  is  about  30,000 
miles.  Within  the  embrace  of  the  great  curve,  and  rising 
from  the  deeply  submerged  floor  of  the  Pacific,  are  many 
volcanic  islands  and  still  active  craters. 

A  branch  of  the  western  arm  of  the  volcanic  system 
just  referred  to,  embraces  Java,  Sumatra,  etc.  A  corre- 
sponding offshoot  of  the  eastern  arm  is  marked  by  the 
volcanoes  of  the  West  Indies. 

It  is  a  matter  of  observation  that  the  loftiest  mountains 
of  a  continent  face  the  largest  ocean  washing  its  shores. 
In  a  similar  wa.y  it  may  be  remembered  from  a  study  of 
the  distribution  of  volcanoes,  that  the  greatest  volcanic 
belt  in  the  world  embraces  the  largest  ocean.  Whether 
this  association  indicates  an  essential  or  genetic  connec- 
tion between  the  height  of  mountains  or  the  prevalence 
of  volcanoes,  and  the  extent  of  water  bodies,  remains  to 
be  shown. 

The  volcanic  areas  considered  in  this  book  form  a  part 
of  the  great  Pacific  belt,  but  include  an  exceptional  por- 
tion of  it,  since  from  Central  Mexico  to  southeastern 
Alaska  there  are  no  active  vents.  In  this  interval  of 
some   four    thousand   miles,   however,   there    are   many 


-'::T  -*-rr'--.rr'j*iFjsa=-- 


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DISTUIIJUTIOX   OF    VOLCANOES 


129 


recently  extinct  craters,  as  well  as  hot  springs  and  gey- 
sers. It  is  in  this  break  in  the  chain  of  steaming  craters 
that  the  breadth  of  the  volcanic  belt  is  greatest.  This 
coincidence  is  significant,  as  will  be  .shown  in  advance. 

An  examination  of  the  accompanying  ma})  of  North 
America,  Plate  4,  in  which  the  positions  of  most  of  the 
active  and  recently  extinct  volcanoes  are  indicated,  will 
show  that  our  studies  are  to  be  confined  to  the  Avestern 
portion  of  the  continent,  and  for  the  most  part,  to  the  im- 
mediate border  of  the  Pacific.  No  volcanoes  sufficiently 
recent  to  be  recognized  by  their  topographic  forms  occur 
east  of  the  sharply  defined  eastern  border  of  the  Cordil- 
leran  mountain  series.  The  central  and  eastern  portions 
of  the  United  States,  the  central,  eastern,  and  northern 
portions  of  Canada,  and  mnch  of  Alaska,  excepting  its 
immediate  southern  border,  are  without  evidence  of  recent 
volcanic  activity.  No  active  or  recentl}'  extinct  volcanoes 
have  been  discovered  in  the  Greenland  region.  Iceland, 
as  is  well  known,  is  an  active  volcanic  centre,  but,  as 
stated  in  the  introduction,  is  not  included  in  our  present 
studies. 

The  most  recent  volcanic  rocks  in  all  of  the  vast  region 
just  referred  to  —  east  and  north  of  the  Cordilleran  series 
and  embracing  five-sixths  of  North  America  —  are,  so  far 
as  known,  confined  to  the  Atlantic  border  and  occur  in 
the  Newark  system.  Some  accounts  of  these  rocks  have 
already  been  given  in  connection  with  other  igneous  intru- 
sions. They  were  poured  out  in  part  as  molten  lavas 
during  the  Mesozoic  era,  or  the  middle  *age  of  the  earth's 
geological  history.  Erosion  has  been  so  great  since  the 
volcanoes  from  which  they  came  were  in  activity  that 
scarcely  a  vestige  of  the  cinder  cones  or  of  the  mountains 


^^^^^Krmm 


130 


VOLCANOES  OF  NORTH   AMEUTCA 


ii 


<! 


they  formed  now  remains.  Tlic  prejjorvation  of  such 
records  as  still  exist  is  due  to  the  fact  that  the  volcanic 
rocks  wore  buried  beneath  sedimentary  deposits  and,  for 
a  very  long  period,  so  depressed  that  they  were  below 
the  ocean's  level,  and  thus  escaped  removal  by  erosive 
agencies. 

Still  more  remote  in  the  earth's  history,  volcanic  erup- 
tions on  a  grand  scale  occurred  in  what  is  now  the  Appa- 
lachian region  and  in  the  Lake  Superior  basin.  These 
ancient  volcanoes  are  far  beyond  the  horizon  that  limits 
the  view  presented  in  these  pages.  They  illustrate  the 
fact,  however,  that  even  in  the  remote  past  volcanoes 
were  situated  on  continental  borders.  When  the  vents 
from  which  the  rocks  referred  to  were  derived,  were  in 
activity,  the  continent  had  increased  but  little  from  its 
original  Archaean  nucleus,  and  the  sea  occupied  the  whole 
of  what  is  now  the  Mississippi  valley  and  the  northward 
extension  of  the  same  interior  basin  to  the  Arctic  regions. 

The  volcanic  mountains  with  which  we  are  now  inter- 
ested are  nearly  all  of  post-Tertiary  age.  Some  of  the 
lava  flows  of  Idaho,  Washington,  etc.,  however,  which 
we  will  have  occasion  to  study,  were  poured  out  during 
the  Tertiary  and  were  buried  beneath  the  sediments  of 
great  lakes,  the  date  of  which  is  recorded  by  the  fossils 
they  contain. 

The  portion  of  the  Pacific  volcanic  belt  along  which 
I  wish  to  take  the  reader,  is  only  a  score  of  miles  wide 
in  Central  America,  but  broadens  in  the  central  part  of 
Mexico  somewhat  abruptly  to  about  800  miles,  and 
touches  both  the  Gulf  and  Pacific  coasts.  A  gradual 
increase  in  breadth  occurs  north  of  Mexico,  and  in  the 
latitude  of  San  Francisco  and  Denver  it  attains  its  maxi- 


I 

f 


DISTUinUTION    OF    VOLC.'ANOKH 


131 


m;  m  width  — 1000  miles.  When  followed  northward, 
it  again  contracts,  and  in  Alaska  is  as  narrow  and 
sharply  defined  as  in  Central  America.  The  narrow 
tapering  sonthern  extremity  of  this  voleanic  helt  curves 
eastward ;  its  similar  northern  extremity,  which  also  row- 
tracts  in  hreadth  towards  its  extremity,  curves  westward. 

It  is  a  significant  fact  that  it  is  in  the  narrow,  curved 
extremities  of  this  volcanic  helt  that  volcanii;  eruptions 
have  occurred  most  recently,  and  where  all  of  the  still 
active  volcanoes  of  North  America  are  situated.  In  the 
broader  and  less  curved  central  portion,  only  extinct 
volcanoes  occur. 

Recent  as  has  been  the  migration  of  civilized  people 
into  North  America,  they  have  witnessed  volcanic  out- 
breaks that  are  scarcely  second  to  any  that  have  occurred 
elsewhere  on  the  earth  during  the  same  period.  In  some 
instances,  volcanoes  have  been  born  and  grown  to  be 
lofty  mountains,  with  all  the  symmetry  and  grace  of 
youth,  since  white  men  have  occupied  the  land  of  their 
nativity.  Neighboring  mountains,  built  by  similar  forces 
in  more  distant  times,  exhibit  the  unmistakable  marks 
of  age.  Their  summits  show  but  faint  signs  of  the  heat 
that  once  caused  vast  columns  of  steam  to  ascend  above 
them.  Others  in  the  same  series  are  cold  and  their 
craters  overgrown  with  vegetation,  or  occupied  by  lakes, 
and  even  filled  with  snow  and  glacial  ice.  This  succes- 
sion from  youth  to  old  age  is  illustrated  by  an  abundance 
of  examples  in  the  region  we  are  to  explore,  and  will 
enable  us  to  sketch,  in  outline  at  least,  the  normal  life 
history,  as  it  may  be  termed,  of  a  volcanic  mountain. 

The  task  we  have  undertaken  is  not  only  to  learn  the 
distribution  of  volcanoes  in  North   America,  and  which 


T 


wm 


]■ 


:  ,' 


132 


VOLCANOES   or   NORTH   AMERICA 


are  active  and  which  extinct,  and  the  dates  of  their 
eruptions,  the  height  and  forms  of  the  piles  of  ejected 
material  of  which  they  are  composed,  etc..  but  to  study 
the  changes  that  volcanic  piles  pass  ^  hrough,  from 
the  time  subterranean  forces  lead  to  ir  birth  and 
growth,  to  the  time  when  the  destructive  agencies  of 
the  air  remove  such  portions  of  them  as  are  above  sea 
level. 

These  studies  of  the  changes  in  progress  on  the  earth's 
surface  lead  directly  to  the  consideration  of  still  greater 
problems,  —  such  as  the  origin  of  volcanoes,  the  relation 
of  surface  extrusions  of  molten  rock  to  subterranean 
intrusions  which  form  dikes,  intruded  sheets,  cistern-like 
intrusions  known  as  laccolites,  and  the  origin  of  still 
greater  dome-like  uplifts  due  to  an  injection  of  plastic 
inaterial  b'^neath  and  termed  subtuberant  mountains. 
Beyond  these  problems,  but  intimately  connected  with 
them,  is  the  consideration  of  the  condition  of  the  earth's 
interior,  the  reaction  of  the  earth's  crust  on  its  still 
highly  heated  central  portion  as  cooling  progresses,  the 
origin  of  continents,  ocean  basins,  mountain  ranges,  etc. 
It  is  not  to  bo  hoped,  from  what  is  now  known  concern- 
ing the  volcanoes  of  North  America,  that  we  will  be  able 
to  answer  satisfactorily  all  of  the  questions  which  sug- 
gest themselves  in  this  connection,  but  we  shall,  I  trust, 
be  better  abL  to  understand  the  limiting  conditions  of 
these  great  problems  and  see  them  from  various  points 
of  view.  What  is  known  concerning  the  volcanic  his- 
tory of  the  earth  is  certainly  small  in  comparison  with 
the  portion  still  unknown.  The  hope  of  discovery 
should,  therefore,  stimulate  the  student  at  every  step 
in  this  branch  of  nature  study. 


,v.. 


.  I.'  "-"J mil 


T 


W 


DISTRIBUTION   OF   VOLCANOES 


133 


"\ 


In  the  study  of  the  volcanoes  of  North  America,  it  is 
convenient  to  recognize  three  geographical  divisions : 
1st,  a  southern  or  Central  American  and  Mexican  region 
of  active  craters;  2d,  a  middle  region  of  extinct  or 
perhaps,  in  part,  dormant  volcanoes,  extending  from 
central  Mexico  through  the  western  part  of  the  United 
States  and  far  into  Canada;  and  3d,  a  northern  or 
Alaskan  region  of  still  steaming  mountains.  The  general 
plan  of  our  studies  will  conform  to  this  arrangement. 


■■<''     I 


iVIJ,  ^  JL-ir-^A^  ,|H  J.i.-IBUa.l. 


,uu  ai  v-i^«"w»BPw»i 


T 


i; 


CHAPTER  III 


VOLCANOES   OF  CENTRAL  AMERICA 


'I' 


'il 


11 


i 


1 


u 


1.1 


( The  principal  volcanoes  of  Central  America  are  indicated  on  the  map  form- 
ing Plate  4.) 

North  and  South  America  are  connected  by  an  isthmus 
the  narrowest  portion  of  which,  barely  twenty-two  miles 
broad,  is  near  its  junction  with  the  southern  continent. 
It  is  there  that  the  dividing  line  between  the  two  conti- 
nents of  the  New  World  is  most  naturally  drawn.  This 
division  is  the  most  natural  one  also  in  reference  to  the 
distribution  of  volcanoes,  since  in  the  Province  of  Pan- 
ama there  is  a  break  in  the  great  Pacific  volcanic  belt. 

Popular  descriptions  of  the  volcanoes  of  Central  America 
can  be  had  in  larger  number,  since  volcanic  mountains  in 
most  instances  are  conspicuous  objects,  and  an  eruption 
always  commands  attention,  but  to  the  special  student  a 
f '^w  typical  examples  are  of  more  value  than  a  multiplicity 
of  general  observations.  With  the  exception  of  the  admi- 
rable report  of  Dollfus  and  Mont-Serrat,  and  one  or  two 
less  extensive  accounts  by  trained  observers,  the  literature 
bearing  on  the  geography  and  geology  of  Central  America 
is  lacking  in  scientific  value. 

General  Geography  and  Geology. — The  information  avail- 
able concerning  the  geography  and  geology  of  Central 
America  seems  to  show  that  the  general  features  of  that 
region  resemble  those  of  the  Sierra  Nevada.     Throughout 

134 


VOLCANOES  OF  CENTRAL  AMERICA 


135 


Central  America  there  is  a  tableland  which  presents  a 
gentle  slope  to  the  northeast,  but  terminates  abruptly  on 
the  southwest.  Presumably  this  tableland  is  the  surface 
of  a  tilted  block  of  the  earth's  crust,  or  a  series  of  such 
blocks,  limited  on  the  southwest  by  a  narrow  belt  of 
intersecting  and  branching  fractures.  Tlie  main  struct- 
ural features,  as  just  stated,  resemble  those  of  the  Sierra 
Nevada,  except  that  the  upraised  border  of  the  tableland 
adjacent  to  the  belt  of  fracture,  faces  westward  instead  of 
eastward.  Along  the  belt  of  faulting  adjacent  to  the  west 
coast,  there  are  scores  of  volcanic  mountains  which  give 
to  the  scenery  of  Central  America  its  culminating  points 
and  its  chief  attractions.  The  belt  of  fracture  is  sharply 
defined  and  is  marked  by  hundreds  of  craters,  solfataras, 
and  hot  springs.  Evidently  the  fractures  which  admitted 
of  the  tilting  of  the  eastward  sloping  tableland  reached 
downward  to  regions  where  the  rocks  are  intensely  heated, 
and  furnished  passageways  for  the  escape  of  molten  rock. 
The  region  is  humid  and  the  surface  rocks  are  water- 
charged.  As  the  lava  was  forced  upward  from  deep 
within  the  earth,  it  came  in  contact  with  water,  and  the 
steam  generated  escaped  at  the  surface  in  many  instances, 
with  explosive  violence.  Nearly  all  of  the  volcanoes,  so 
far  as  can  be  judged  from  the  descriptions  available, 
are  of  the  Vesuvian  type,  and  the  elevations  they  have 
produced  are  mainly  the  result  of  the  accumulation  of  pro- 
jectiles. In  numerous  instances,  however,  streams  of  lava 
have  flowed  out,  but  as  is  the  rule  with  most  trachytic 
lava,  the  prevalent  type  in  Central  America  and  Mexico 
did  not  advance  far  or  expand  widely. 

Distribution  of  the  Volcanoes. — The  belt  of  active  and 
recently  extinct  volcanoes,  seldom  over  fifty  miles  broad. 


iS^tetSm 


JJU»U 


i 


■ 

J 

1 

136 


VOLCANOES   OF  NORTH  AMEBICA 


which  skirts  the  Pacific  coast  of  Central  America,  begins 
at  the  south  in  two  prominent  mountains  which  are 
reported  to  be  extinct  volcanoes,  in  the  northern  part  of 
Panama.  These  peaks  are  known  as  Chiriqui  and  Rovalo ; 
tlieir  elevations  are  11,265  and  7021  feet,  respectively. 
Of  these  two  peaks,  the  first  named  is  said  to  be  the  more 
typical  example  of  a  mountain  built  of  extruded  material, 
for  the  reason  that  it  is  a  symmetrical  cone  with  grace- 
fully sloping  sides.  Associated  with  these  two  mountains 
is  a  third,  known  as  Pico  Blanco,  11,740  feet  high,  which 
has  been  reported  by  certain  travellers  to  be  also  of  vol- 
canic origin,  but  is  considered  by  other  observers,  and 
especially  by  W.  M.  Gabb,^  as  a  remnant  left  by  erosion 
of  a  great  porphyritic  dike. 

This  trio  of  mountains,  clothed  with  luxuriant  tropical 
vegetation,  stands  as  a  monument  at  the  southern  end  of 
a  vast  series  of  cones,  craters,  and  lava  flows,  which  ter- 
minates some  seven  thousand  miles  to  the  northwestward, 
in  the  treeless,  desolate,  mist-covered  Aleutian  Islands. 
The  striking  contrasts  in  the  present  aspects  of  nature 
encountered  as  one  traverses  this  volcanic  belt  from  end  to 
end,  prepares  one  in  a  measure  for  the  wonderful  chapters 
of  peace  and  war  in  the  life  history  of  our  continent, 
revealed  when  its  geology  and  geography  are  studied. 

The  volcanoes  of  Central  America  have  not  been 
thorouglily  explored,  but  to  bring  together  all  of  the  scat- 
tered observations  made  by  travellers  and  by  the  few 
traiued  observers  who  have  visited  the  region,  would  lead 
to  a  great  mass  of  details  in  which  it  would  be  difficult  to 
trace  a  connection.    I  shall,  therefore,  present  a  list  of  the 

1  "  Notas  on  Costa  Rica  Geography,"  in  "American  Journal  of  Science," 
Vol.  9,  3d  Series,  1875,  pp.  198-204. 


VOLCANOES   OF   CENTRAL   AMERICA 


137 


best  known  volcanoes,  accompanied  by  a  few  facts  respect- 
ing their  height  and  the  dates  of  the  latest  eruptions, 
taken  principally  from  Brigham's  admirable  narrative  of 
his  tra/els  in  Guatemala,^  and  follow  this  with  a  some- 
what detailed  account  of  a  few  of  the  most  prominent 
and  best  known  volcanoes.  On  the  accompanying  map, 
Plate  4,  for  which  I  am  indebted  largely  to  the  book  just 
referred  to,  the  distribution  of  Central  American  volcanoes 
is  shown. 

In  the  following  list  of  Central  American  volcanoes,  so 
far  as  practicable,  their  order  from  southeast  to  northwest 
is  indicated. 

List  of  the  Active  and  Recently  Extinct  Volcanoes 

OF  Central  America 


Namb. 


IN   COLOMBIA 

Present 

State. 


Chiriqui ? 

Kovalo ? 

Pico  Blanco Extinct 


Last 
Eruption. 


Height.'^ 

Feet. 

.  11,265 
.  7,021 
.  11,740 


IN   COSTA   RICA 

Chiripo Extinct 

Tvirrialba Extinct 12,523 

Irazu,  or  Cartago Active     .     .     .     1726  .     .     .  11,450 

Barba Extinct 

Los  Votos,  or  Poas    ....  Extinct 10,500 

Tenorio Extinct 

Miravalles Extinct 5,500 

Rincon  de  la  Vieja    ....  Quiescent 

Orosi Quiescent 8,650 

^  W.  T.  Brigham,  "Guatemala,  the  Land  of  the  Quetzal,"  New  York, 
1887. 

2  The  heights  given  cannot  be  considered,  in  most  instances,  as  more  than 
approximately  correct. 


138 


VOLCANOES  OF  NORTH  AMERICA 


li, 


Name. 


IN  NICARAGUA 

Present 

State. 


Madeira Quiescent 

Onietepe       Active 

Zapeton,  or  Zapatera     .     .     .  Extinct 

Mombacho Extinct 

Masaj'a Active 

Nindiri Quiescent 

Guanapepe Extinct 

Momotombito Extinct 

]\Iomotombo Active 

Axusco,  or  Asososco  ....  Extinct 

Las  Pilas Quiescent 

Orota Quiescent 

Telica Active     . 

Santa  Clara Quiescent 

El  Viejo Quiescent 

Chonco Quiescent 

Couseguina Quiescent 


IN   HONDURAS 


Last 
Eruption. 


1883 


1858 


1852 


1850 


1835 


Height. 

Feet. 

5,000 
5,050 

5,250 
3,000 


7,000 
4,690 
4,000 

3,800 
4,700 
5,562 

3,600 


Bay  Islands Extinct  . 

Bonito Quiescent 

Congrehoy  Peak Quiescent 

Tigre Extinct  . 

Zacate  Grande Extinct  . 


1,000 

8,040 
2,632 
2,000 


.\^ 


.  ,ii 


IN   SAN  SALVADOR 

Conchagua Quiescent 3,915 

San  Miguel Active     .     .     .     1844  .    .     .  6,244 

Chinameca Quiescent 5,000 

Usulutan Extinct  ........ 

Tecapa Extinct 

San  Vicente Quiescent    .     .     1643  .     .     .  7,600 

Cojutepeque,  or  Ilopango  .     .     Active 3,400 

San  Salvador Active 6,182 

Izalco Active     .     .     .    Constant     .  6,000 

Santa  Ana Active 6,000 

Apaneca Extinct 5,826 


ii 


.\^ 


VOLCANOES   OF  CEXTUAL  AMERICA 


181) 


IN   GUATEMALA 


Name. 


Present 

State. 


Last 
Ehuption. 


Ipala 

Monte  Rico 

Suchitan,  or  Santa  Catarina 

Mita 

Aniayo 

Chingo 

Moyuta 

Tecuamburro 

Cerro  Kedondo      .... 
Pacaya  (Pecul)      .... 

Agua 

Fuego 

Acatenango 

Atitlan 

San  Pedro    

Santa  Clara 

Zuilil 

Cerro  Quemado     .... 
Santa  Maria  (Exancul)  .     . 

Tajamulco 

Tacana 


Height. 

Ffft. 

Extinct 5,460 

Extinct 

Extinct   .     .     .     14G9?     .     . 

Extinct 5,000 

Extinct 

Extinct 6,500 

Extinct 

Extinct 

Extinct 3,550 

Quiescent    .     .     1775  .     .     .    8,390 

Extinct 12,337 

Active     .     .     .     1880  .     .     .  12,075 

Quiescent 13,563 

Active     .     .     .     1852  .     .     .    9,870 

Extinct 8,125 

Extinct 8,554 

Extinct 

Quiescent    .     .     1785  .     .     .10,205 

Extinct 11,415 

Extinct 18,317? 

Quiescent    .     .     1855  .     .     .  11,500 


From  this  list  let  us  select  a  few  of  the  best  known  and 
most  characteristic  examples  of  volcanic  phenomena  for 
special  study. 

Young  Volcanoes 

At  a  few  localities  in  various  countries,  as  shown  by 
historic  records,  fissures  have  opened  in  the  earth,  accom- 
panied by  earthquakes,  and  the  escape  of  steam  and 
molten  rock,  together  with  other  phenomena  characteristic 
of  volcanoes,  at  localities  where  similar  disturbances  were 
previously  unknown.  In  some  of  the  instances  referred 
to,  the  ejected  material  has  accumulated  about  the  opening 


V 


140 


VOLCANOES  OF  NORTH  AMEllICA 


■ 


M, 


from  which  it  was  discharged,  until  a/ conspicuous  hill, 
and  even  a  mountain-like  volcanic  pile,  has  resulted.  Not 
only  have  the  births  of  volcanoes  been  observed,  but  also, 
in  a  few  instances,  their  growth  and  action,  until  their 
energy  has  l)een  expended  and  the  span  of  their  brief 
existence  terminated. 

One  volcanic  hill,  named  Monte  Nuovo,^  the  history  of 
which  is  well  known,  is  situated  in  Italy  between  historic 
Lake  Avernus  and  Baice  Bay.  This  mountain,  as  it  is 
termed,  came  into  existence  in  1538,  soon  attained  a  height 
of  440  feet,  and  then  became  extinct.  A  drive  from 
Naples  through  a  charming  region  will  enable  one  to  visit 
it  and  return  in  a  single  day. 

Although  Monte  Nuovo  is  cited  as  the  type  of  a  young 
volcanic  mountain  in  many  books  of  geography  and 
geology,  and  serves  as  an  illustration  of  the  manner  in 
which  molten  material  is  extruded  from  the  interior  of 
the  earth  so  as  to  make  conspicuous  surface  changes,  it  is 
by  no  means  as  impressive  an  example  of  elevations 
built  by  volcanic  forces  within  historic  times,  as  three  or 
four  similar  occurrences  that  have  been  witnessed  in  the 
New  World.  I  refer  to  the  young  but  still  active  volcano 
in  San  Salvador,  known  as  Izalco,  which  came  into  exist- 
ence in  1770 ;  a  nameless  volcano  in  Nicaragua,  the  first 
eruption  of  which  was  witnessed  by  the  American  travel- 
ler, E.  G.  Squier,  in  1850  ;  an  eruption  in  the  centre  of 
Lake  Ilopango,  San  Salvador,  in  1879  ;  and  the  birth  of 
Jorullo,  in  Mexico,  in  1759.  As  these  young  volcanoes 
have  features  of  general  interest  which  supplement  each 


^* 


*  An  account  of  the  origin  and  brief  history  of  Monte  Nuovo  may  be 
found  in  Lyell's  "Principles  of  Geology,"  11th  edition,  New  York,  1874, 
Vol.  I,  pp.  607-619. 


VOLCANOES  OF  CENTUAL   AMEUICA 


141 


othor,  it  is  convenient  to  break  the  geographic  order 
of  our  studies  and  consider  them  together. 

Izalco.  —  The  still  active  volcano  known  as  Izalco, 
about  thirty  miles  west  of  the  city  of  San  Salvador, 
is  now  ap[)roximately  3000  feet  in  height  above  the  sur- 
rounding country,  and  rises  about  5000  feet  above  sea 
level.  Its  prominence  in  the  region  in  which  it  stands 
is  due  to  the  accunuilation  of  lava,  scoria,  and  lapilli 
about  a  centre  of  eruption,  which  first  showed  evidence  of 
volcanic  activity  in  1770.  The  appearance  of  the  cone  of 
Izalco  in  1894  is  shown  in  Plate  5. 

Accounts  of  the  birth  and  growth  of  Izalco  have  been 
given  by  numerous  writers,  and  especially  by  Humboldt, 
and  within  recent  years,  by  Stephens,  Squier,  and  Dollfus 
and  Mont-Serrat.^ 

The  account  of  this  remarkable  volcano  given  by  Squier 
in  his  essay  on  the  volcanoes  of  Central  America,  reads  as 
follows : 

"It  arose  from  the  plain  in  1770,  and  covers  what  was 
then  a  fine  cattle  hacienda  or  estate.  The  occupants  on 
this  estate  were  alarmed  by  subterranean  noises  and 
shocks  of  earthquakes,  about  the  end  of  1769,  which  con- 
tinued to  increase  in  loudness  and  strength  until  the  23d 
of  the  February  following,  when  the  earth  opened  about 
half  a  mile  from  the  dwellings  on  the  estate,  sending  out 

1  A.  von  Humboldt,  "Cosmos,"  New  York,  1869,  Vol.  V,  pp.  248,249, 
2G1.  J.  L.  Stephens,  "Incidents  of  Travel  in  Central  America,"  [etc.]. 
New  York,  1841,  Vol.  T,  pp.  .325-330.  There  have  been  many  editions  of 
this  work.  E.  G.  Squier,  "  The  States  of  Central  America,"  New  York, 
18.58,  pp.  296,297;  "On  the  Volcanoes  of  Central  America"  [etc.],  in 
American  Association  for  the  Advancement  of  Science,  Proceedings,  New 
Haven  meeting,  1850,  pp.  101-122.  A.  Dollfus  et  E.  de  Mont-Serrat,  "Voy- 
age geologique  dans  les  republiques  de  Guatemala  et  de  Salvador,"  Paris, 
1868,  pp.  376-406. 


TS? 


w 


^ 


142 


VOLCANOES  OF   NORTH   AMERICA 


» 


lava,  accompanied  by  fire  and  smoke.  The  inhabitants 
fled  ;  but  the  vaqueros,  or  herdsmen,  who  visited  the  estate 
daily,  reported  a  constant  increase  in  the  smoke  and  flame, 
but  that  the  ejection  of  lava  was  at  times  suspended,  and 
vast  quantities  of  ashes,  cinders,  and  stones  sent  out 
instead,  forming  an  increasing  cone  around  the  vtMit,  or 
crater.  This  process  was  continued  for  a  long  period,  but 
for  many  years  the  volcano  has  thrown  out  no  lava.  It 
has,  however,  remained  in  a  state  of  constant  eruption, 
the  explosions  occurring  every  sixteen  minutes  and  a 
quarter,  with  a  noise  like  the  discharge  of  a  park  of  artil- 
lery, accompanied  by  a  dense  smoke  and  a  cloud  of  ashes  and 
stones,  which  fall  upon  every  side,  and  add  to  the  height 
of  the  cone.  It  is  now  about  1500  or  2000  feet  in  height, 
and  1  ..m  informed  by  an  intelligent  West  Indian  gentle- 
man, Dr.  Drivon,  who  has  known  it  for  the  past  twenty- 
five  years  [previous  to  1850],  that  within  that  period  it 
has  increased  about  one-third.  At  some  times  tlie  explo- 
sions are  more  violent  than  at  others,  and  the  ejected 
matter  greater  in  amount ;  but  it  is  said  the  discharges 
are  always  regular.  With  the  wind  in  a  favorable  direc- 
tion, an  annoying  and  sometimes  injurious  quantity  of 
fine  ashes  or  powder  is  carried  to  the  city  of  Sonsonate, 
twelve  miles  distant." 

An  extinct  volcano  near  Izalco  was  ascended  by 
Stephens  in  January,  1840,  who  gives  in  his  well-known 
work  of  travel,  already  referred  to,  a  graphic  account  of 
the  appearance  of  the  active  crater  as  seen  from  above. 
From  Sonsonate  he  heard  the  noise  of  the  eruption  of  the 
volcano  during  the  daytime  and  at  night  saw  the  light  of 
the  crater  and  the  streams  of  lava  rolling  down  its  sides. 
Passing  the  town  of  Izalco,  the  travellers,  quoting  from 


1 


■ 


vor.r.woKs  ov  noimm   xmiiimi  \. 


I'l  Air.  -. 


] 


Izulcii,  Mill  Siilviulor,  l.y.t4. 


i| 


VOLCANOES   OF  CENTRAL   AMERICA 


143 


the  narrative  referred  to,  "soon  canio  out  on  an  open 
plain,  and  witliout  a  bush  to  olMtriU't  the  view,  and  saw 
on  our  It'ft  the  vvliole  volcano  from  its  base  to  its  top.  It 
rose  from  near  the  fo(.)t  of  a  mountain,  to  a  height  per- 
haps of  3000  feet,  its  sides  brown  and  barren,  and  all 
around  for  miles  the  earth  was  covered  with  lava.  Heiug 
in  a  state  of  eruption,  it  was  impos.sible  to  ascend  it,  but 
behind  it  is  a  higher  mountain,  which  counnands  a  view 
of  the  burning  crater.  The  whole  volcano  was  in  full 
sight,  .spouting  into  the  air  a  column  of  black  smoke  ami 
an  immen.se  body  of  stones,  while  the  earth  shook  under 
our  feet.  .  .  .  We  came  out  suddenly  upon  an  ojien 
point,  higher  than  the  top  of  the  volcano,  commanding  a 
view  of  the  interior  of  the  crater,  and  so  near  it  that  wt? 
saw  the  liuge  stones  as  they  separated  in  the  air,  and  fell 
pattering  around  the  sides  of  the  volcano.  In  a  few 
minutes  our  clothes  were  white  with  ashes,  which  fell 
around  us  with  a  noise  like  the  sprinkling  of  rain. 

"  The  crater  had  three  orifices,  one  of  which  was 
inactive ;  another  emitted  constantly  a  rich  blue  smoke  ; 
and  after  a  report,  deep  in  the  huge  throat  of  the  third 
appeared  a  light  blue  vapor,  and  then  a  mass  of  thick 
black  smoke,  whirling  and  struggling  out  in  enormous 
wreaths,  and  rising  in  a  dark  majestic  column,  lighted  for 
a  moment  by  a  sheet  of  flame  ;  and  when  the  smoke  dis- 
persed, the  atmosphere  was  darkened  by  a  shower  of 
stones  and  ashes.  This  over,  a  moment  of  stillness  fol- 
lowed, and  then  another  report  and  eruption,  and  these 
continued  regularly,  at  intervals,  as  one  guide  said,  of 
exactly  five  minutes,  and  really  he  was  not  much  out  of 
the  way.  .  .  . 

"  The  cure  of  Sonsonate,  still  in  the  vigor  of  life,  told 


I'fl 


^^m 


I 


h 


•I? 


'l 


li 


144 


VOLCANOES   OP   NORTH   AMERICA 


me  that  lie  remembered  when  the  ground  on  which  this 
volcano  stands  had  nothing  to  distinguish  it  from  any 
other  spot  around.  In  1798,^  a  small  orifice  was  dis- 
covered puffing  out  small  quantities  of  dust  and  pebbles. 
He  was  then  living  at  Izalco,  and,  as  a  boy,  was  in  the 
habit  3f  going  to  look  at  it ;  and  he  had  watched  it  and 
had  marked  its  increase  from  year  to  year  until  it  Ind 
grown  into  what  it  is  now.  .   .  ." 

The  next  account  we  have  of  this  young  and  still 
energetic  volcano  is  by  Dollfus  and  Mont-Serrat,  who, 
finding  it  in  a  state  of  mild  activity  in  1866,  climbed  to 
its  summit  and  made  a  survey  and  study  of  its  environ- 
ments. This  is  by  far  the  most  complete  and  scientific 
description  of  the  mountain  available,  but,  to  avoid  repe- 
tition, only  a  few  notes  of  features  of  special  interest 
will  be  taken  from  it. 

On  leaving  Sonsonate,  the  travellers  crossed  a  basaltic 
plain  covered  nearly  everywhere  with  decomposed  vol- 
canic dust  and  lapilli,  on  which  grew  dense  forests.  At 
the  immediate  foot  of  the  volcano,  a  black,  desolate  zone, 
in  general  five  to  six  hundred  metres  broad,  completely 
surrounded  it.  This  lava  field  appears  to  have  been  a 
lake  of  molten  rock  without  motion,  and  to  have  acquired 
a  rough,  scoriaceous  surface  on  cooling  and  hardening. 
Near  the  base  of  the  cone,  the  surrounding  basalt  has 
an  upward  slope  toward  the  volcano,  of  two  or  three 
degrees,  and  exhibits  also  a  more  markedly  scoriaceous 
surface.  As  one  approaches  still  nearer  the  base  of  the 
volcano,   the   upward   inclination   increases   to   such    an 


*  There  is  a  discrepancy  between  this  and  other  dates  given  for  the 
beginning  of  the  eruptions.  What  seem  to  be  the  most  reliable  records 
place  it  in  1770,  as  stated  above. 


I 


VOLCANOES   OF  CENTRAL  AMERICA 


145 


extent  as  to  make  it  seem  as  if  the  actual  climb  had 
begun. 

Before  the  base  of  the  volcano  is  reached,  the  lava 
gradually  disappears  beneath  a  covering  of  loose,  angu- 
lar rocks,  and  of  smooth,  rounded  bomlis  with  black, 
vitreous  surf;<ces.  This  coarse  material,  varying  in  gen- 
eral from  the  size  of  one's  hand  to  a  cubic  metre,  came 
from  the  crater  above  and,  rolling  down  its  sides,  formed 
a  circle  about  its  base. 

The  cone  itself,  at  the  date  referred  to,  was  284  metres 
hijjh  above  its  immediate  base  on  the  north  and  400 
metres  on  the  south  side.  It  is  composed  of  small,  scoria- 
ceous  fragments  (lapilli,  volcanic  gravel,  and  dust)  ejected 
from  the  summit  and  deposited  in  layers  which  slope 
away  from  the  crater  rim  in  all  directions.  The  cone 
is  described  as  perfect  in  form  and  of  graceful  shape,  — 
so  regular  and  smooth,  in  fact,  that  it  gives  one  the  im- 
pression of  having  been  turned  in  a  lathe.  The  sides  slope 
at  angles  of  35°  and  even  of  40°.  Such  slopes  are  diffi- 
cult of  ascent,  even  when  firm,  but  when  composed  of 
loose,  incoherent  lapilli,  into  which  one  sinks  more  than 
ankle  deep  at  each  step,  the  climb  becomes  exceedingly 
fatiguing.  No  pumice  was  seen,  but  the  fragments  of  lava 
were  frequently  scoriaceous,  light,  and  rough  in  texture,  and 
varying  in  color  from  red  through  many  shades  of  brown  to 
black.  Some  of  the  black  specimens  resembled  fragments 
of  coke,  having  the  same  shining  fissures  and  metallic  lus- 
tre. The  lapilli  became  finer  toward  the  summit  and  were 
there  coated  with  sulphurous  and  aluminous  incrustations 
which,  from  a  distance,  resembled  patches  of  snow. 

On  reaching  the  summit,  the  explorers  ^^ound  it  to 
differ  but   little  from  its  condition  in    1840,  when  seen 


146 


VOLCANOES   OF    NUKTH    AMERICA 


[I  ■'■! 


h     I 


I*  i '  r 
1  ' '  . 


I 'I 


I' 

I 

I     ii 

.Mi 


by  Stophons  from  a  neigliboring  eminence.  There  were 
three  craters,  the  central  one  being  tlie  hirgest  and  most 
active ;  and  from  it  a  great  vohnne  of  vapor,  darkened 
at  times  by  dust  shot  upwards  by  explosions,  was  rolling 
out.  This  was  a  funnel-shaped  depression  eighty  metres 
in  diameter  and  about  twenty-five  metres  deep.  At  its 
bottom  there  was  a  rectangular  opening,  like  the  mouth 
of  a  mining  shaft,  four  by  five  metres  in  diameter,  which 
led  down  to  an  unknown  depth.  From  deep  within  this 
shaft  came  continually  dull,  rumbling  sounds,  as  of  steam 
escaping  under  high  pressure.  There  were,  besides,  from 
time  to  time,  quite  violent  detonations  like  distant  thun- 
der, occurring  at  intervals  of  fifteen  minutes.  Accom- 
panying each  of  these  disturbances,  the  vapor  escaped 
with  increased  violence.  Still  other  explosions,  less  pro- 
nounced liut  accompanied  by  a  .shaking  of  the  ground, 
occurred  at  intervals  of  five  minutes. 

One  of  the  most  instructive  of  the  phenomena  observed 
was  the  escape  of  the  heated  va}i(trs  and  gases  at  many 
points  through  the  loose  lapilli.  These  fumaroles  could 
be  divided  in  a  general  way  into  two  classes,  witii  ref- 
erence to  temperature  and  tlie  nature  of  the  emerging 
gases  and  vapors.  The  gases  from  the  hotter  orifices, 
ranging  in  temperature  as  high  by  estimate  as  400", 
were  transparent  or  of  a  bluish  color,  and  consisted 
principally  of  hydrochloric  acid.  The  second  series,  v/ith 
temperatures  of  96"  to  273°,  emitted  white  vapors  which 
consisted  largely  of  steam,  with  hydrochloric,  sulpliuric, 
and  other  gases  mingled  with  it.  Steam  seems  to  have 
been  only  a  minor  feature  of  the  fumaroles.  It  is  stated 
that  rune-tenths  of  the  exhalations  consisted  ut  hydro- 
chloric acid. 


T*m  >  *SFi.«V'i"        KiJt»¥4»  wCaai^^>*  *.  V 


VOLCANOES    OF   CENTRAL   AMERICA 


147 


Fifteen  days  after  tlie  visit  of  DoUfus  and  xMont-Serrat, 
Izalco  was  again  in  a  state  of  violent  eruption. 

Birth  of  a  Volcano  in  Lake  Ilopango,  Salvador.  —  Lake 
llopango,  in  tlie  central  part  of  Salvador,  was  the  centre 
of  a  violent  earthquake  in  1879,  which  was  followed  by 
a  rapid  discharge  of  the  water  of  the  lake.  In  the  course 
of  fifty-four  days  the  lake  fell  thirty-five  feet,  and  dis- 
charged a  volume  of  water  through  a  surface  channel, 
estimated  at  over  20,320  million  cubic  feet.  During  the 
earthquake  the  lake  was  greatly  agitated,  and  immense 
volumes  of  steam  rose  from  its  central  portion.  On  Janu- 
ary 20,  1880,  at  eleven  o'clock  in  the  evening,  a  renewal 
of  the  disturbance  of  the  water  was  noticed,  and  the  next 
morning  a  pile  of  rocks  was  seen  in  the  centre  of  the  lake, 
from  wliich  rose  a  huge  column  of  vapor.  The  eruption 
continued  for  more  than  a  month ;  the  island  of  rocks  in- 
creased in  size,  and  from  it  rose  continuously  a  vapor 
column  fully  a  thousand  feet  high.  The  waters  of  the 
lake  became  heated,  and  sulphurous  vapors  were  emitted 
in  such  abundance  as  to  be  unpleasant  when  the  wind 
blew  from  the  east,  in  the  city  of  San  Salvador,  about 
ten  miles  distant. 

Pre"  ious  to  the  disturbances  just  mentioned,  Lake  Ilo- 
pango was  abundantly  stocked  with  fishes,  which  were 
killed  at  an  earlv  sta'/e  of  the  outbreak.  When  the  erup- 
tion  terminated,  the  island  tliat  had  been  formed  was 
found  to  have  an  area  of  about  five  acres,  and  a  height 
of  160  feet.  In  its  immediate  vicinity  soundings  showed 
a  depth  of  100  ffithoms  of  water. 

Tho  region  all  about  Lake  Ilopango  is  composed  (jf 
volcanic  rocks,  and  judging  from  the  accounts  available, 
the  most  authentic  of  wliich  is  a  report  by  Edwin  Rock- 


148 


VOLCANOES    OF   NOUTII    AMERICA 


I 


M' 


i 


stock  to  the  government  of  Guatemala  (San  Salvador, 
1880),  it  seems  as  if  the  lake  occupies  an  ancient  crater 
or  perhaps  a  depression  due  to  subterranean  explosions, 
the  outlet  of  which  had  been  dammed  by  landslides.  The 
partial  drainage  of  the  lake,  as  well  as  the  formation  of 
a  volcanic  island  in  its  centre,  are  among  the  changes 
of  greatest  geographical  interest  that  accompanied  the 
eruption. 

A  Nameless  Volcano  in  Nicaragua.  —  In  the  account  of 
the  volcanoes  of  Central  America  given  by  Squier,  already 
referred  to,  there  is  an  interesting  description  of  the 
breaking  forth  of  a  new  crater  in  the  beautiful  Plain  of 
Leon  to  the  southwest  of  Lake  Nicaragua.  This  unique 
phenomenon  is  described  as  follows : 

'"  In  fact,  1  have  been  a  personal  witness  of  the  origin 
of  a  new  volcano,  which,  if  it  does  not  meet  a  premature 
extinguishment,  bids  fair  to  add  another  high  cone  to 
those  Wiiich  now  stud  the  great  Plain  of  Leon.  .  .  .  On 
the  11th  and  12th  days  of  April  last  [1850],  rumbling 
sounds,  resembling  thunder,  were  heard  in  the  city  of 
Leon,  situated  in  the  centre  of  the  plain  I  have  described. 
They  seemed  to  proceed  from  the  direction  of  the  vol- 
canoes, and  were  supposed  to  come  from  the  great  volcano 
of  Momotombo,  which  often  emits  noises  and  shows  other 
symptoms  of  activity,  besides  sending  out  smoke.  This 
volcano,  however,  on  this  occasion,  exhibited  no  unusual 
indications.  The  sounds  increased  in  loudness  and  fre- 
quency on  the  night  of  the  12th,  and  occasional  tremors 
of  the  earth  were  felt  on  Leon.  Early  on  the  morning 
of  Sunday,  the  13tli,  an  orifice  opened  near  the  base  of 
the  long-extinguished  volcano  of  Las  Pilas.  about  twenty 
miles  distant  from  Leon.     The  throes  of  the  earth  at  the 


I 


'iii 


VOLCANOES    OF    CENTKAL    AMERICA 


149 


time   of   the  outburst  were  very  severe   in   the  vicinity, 
resembling,  from  the  accounts  of  the  natives,  a  series  of 
concussions.      The  precise  point  where  the  opening  was 
made  might  be  said  to  be  in  the  phiin  ;  it  was,  however, 
somewhat  elevated  by  the  lava  which   had  ages   before 
flowed  down  from  the  volcano,  and  it  was  through  this 
bed  of  lava  that  the  eruption    took    place.     No  people 
reside  within  some  miles  of  the  spot ;  consequently  I  am 
not  well  informed  concerning  the  earlier  phenomena  ex- 
hibited by  the  new  volcano.     It  seems,  however,  that  the 
outburst  was  attended  with  much  liame,  and  that,  at  first, 
quantities  of  melted  matter  were  ejected   irregularly  in 
every  direction.      Indeed,   this   was  clearly  the  case,  as 
was  shown  upon  my  visit  to  the  spot  some  days  there- 
after.    For  a  wide  distance  around  were  scattered  large 
flakes  resembling  freshly  cast  iron.      This  irregular  dis- 
charge continued  only  a  few  hours,  and  was  followed  by 
a  current  of  lava,  which  flowed  down  the  slope  of  the  land 
toward  the  west,  in  the  form  of  a  high  ridge,  rising  above 
the  tops  of  the  trees,  and  bearing  down  everything  which 
onposed  its  progress.     While  this  flow  continued,  which 
it  did  for  the  remainder  of  the  day,  the  earth  was  quiet, 
excepting  only  a  very  slight  tremor,  which  was  not  felt 
beyond  a  few  miles.     Upon  the  14th,  however,  the  lava 
stopped  flowing,  and  an  entirely  new  mode  of  action  fol- 
lowed.    A  series  of  eruptions  commenced,  each  lasting 
about  three  minutes,  succeeded  by  a  pause  of  equal  dura- 
tion.    Each  eruption  was  accompanied  by  concussions  of 
the  earth,  too  slight,  however,  to  be  felt  at  Leon,  attended 
also  by  an  outburst  of  flame  a  hundred  feet  or  more  in 
height.     Showers  of  red-hot  stones  were  also  ejected  with 
each   eruption    to   the    height   of    several    hundred    feet. 


>  it 


i4 


',  I. 

I'  M 


.."-..       .  -ril'B.    •r*>" 


npi 


150 


VOLCANOES   OF    NORTH    AMERICA 


r ; 


Most  of  these  fell  ,  'wk  in  the  mouth  or  cmter,  the  rest 
falling  outward,  and  gradually  building  up  a  cone  around 
it.  By  the  attrition  of  this  process,  the  stones  became 
more  or  less  rounded,  thus  explaining  a  peculiarity  in  tlie 
volcanic  stones  already  alluded  to.  These  explosions  con- 
tinued uninterruptedly  for  seven  days,  and  could  be  accu- 
rately observed  from  Leon  in  the  night." 

Observations  made  by  Squier  and  his  companion.  Dr. 
J.  W.  Livingston,  on  visiting  this  young  volcano,  show 
that  it  presented  on  a  small  scale  many  of  the  phenomena 
to  be  seen  when  Vesuvius  and  other  similar  volcanoes 
are  in  eruption. 

"  In  order  to  obtain  a  full  view  of  the  new  volcano,  we 
ascended  a  high,  naked  ridge  of  scoria,  entirely  overlook- 
ing it.  From  this  point  it  presented  the  appearance  of 
an  immense  kettle,  upturned,  with  a  hole  knocked  in  the 
bottom,  forming  the  crater.  From  this,  upon  one  side, 
ran  off  the  lava  stream,  yet  fervent  with  heat,  and  send- 
ing off  its  tremulous  radiations.  The  eruption  had  ceased 
that  morning,  but  a  volume  of  smoke  was  still  emitted, 
which  the  strong  northeast  wind  swept  down  in  a  trailing 
current  along  the  tree-tops. 

'•  The  cone  was  patched  over  with  yellow,  crystallized 
sulphur,  deposited  from  the  hot  vapors  passing  up  among 
the  loose  stones.  Tlie  trees  all  around  were  stripped  of 
their  limbs,  leaves,  and  bark,  and  resemljled  so  many 
giant  skeletons.  Tempted  by  the  quietude  of  the  volcano, 
and  anxious  to  inspect  it  more  closely,  in  spite  of  the 
entreaties  of  our  guides,  we  descended  from  our  position, 
and  going  to  the  windward  scrambled  over  the  interven- 
ing lava  beds,  through  patches  of  thorny  cactuses  and 
agaves,  toward  the  cone.    On  all  sides  we  found  the  flakes 


VOLCANOES   OF   CENTRAL   AMEIUCA 


151 


•t  '.' 


of  nielted  inutter  wliirli  luid  been  thrown  out  on  the  first 
day  of  tliu  orii[)tioii,  and  which  had  moulded  themselves 
over  whatever  they  lell  upon,  ^ye  had  no  ditliculty  in 
reaching  the  base  of  the  cone,  the  wind  driving  oft"  the 
smoke  and  vapors  to  the  leeward.  It  was  i)erhaps  a  hun- 
dred and  fifty  or  two  hundred  feet  high,  by  two  hundred 
yards  in  diameter  at  the  Ijase,  and  of  great  regularity  of 
outline.  It  was  made  up  entirely  of  stones,  more  or  less 
rounded,  and  of  every  size  from  one  pound  up  to  live  hun- 
dred. No  sound  was  heard  when  we  reached  it,  except  a 
low,  rumbling  noise,  accompanied  by  a  slight  tremulous 
motion.  Anxious  to  examine  it  more  closely,  and  to  tost 
the  truth  of  the  popular  assertion  that  any  marked  dis- 
turbance near  the  volcanic  vents  is  sure  to  bring  on  an 
eruption,  we  proceeded  to  ascend.  Fearing  we  might  find 
the  stones  too  much  heated  near  the  summit.  I  i)repared 
myself  with  two  staffs,  for  support,  and  to  save  my  hands; 
the  doctor  disdained  such  appliances,  and  started  without 
them.  The  ascent  was  very  laborious,  the  stones  rolling 
away  beneath  our  feet,  and  rattling  down  the  sides.  We, 
however,  succeeded  in  almost  reaching  the  sunnnit,  when 
Dr.  Livingston,  who  was  a  little  in  advance,  suddenly 
recoiled  with  an  exclamation  of  pain,  having  all  at  once 
reached  a  layer  of  stones  so  hot  as  to  blister  his  hands  at 
the  first  touch.  We  paused  for  a  moment,  and  I  was 
looking  to  my  footing  when  I  was  startled  by  an  exclama- 
tion of  terror  from  m}-  companion,  who  gave  simultane- 
ously an  almost  superhuman  leap  down  the  side.  At  the 
same  instant  a  strange  roar  almost  deafened  me ;  there 
seemed  to  be  a  whirl  of  the  atmosphere,  and  a  sinking  of 
the  mass  upon  which  i  was  standing.  Quick  as  thought 
I  glanced  upward  ;  the  heavens  were  black  with  stones. 


1 


152 


VOLCANOES   OF   NOUTH    AMKKICA 


\\\ 


n 


and  a  thousand  lightnings  flashed  among  them.  All  this 
was  in  an  instant,  and  in  thu  same  instant  I  too  was 
dasliing  down  the  side,  reaching  the  bottom  at  the  same 
moment  as  my  companion,  and  just  in  time  to  escape  the 
stones,  which  fell  in  rattling  torrents  where  we  had  stood 
a  moment  before.  .  .  .  The  eruption  lasted  for  nearly 
an  hour,  interspersed  with  lulls,  like  long  breathings. 
The  noise  was  that  of  innumerable  blast  furnaces  in  full 
operation,  and  the  air  was  filled  with  projected  and  falling 
stones.  ..." 

For  several  months  after  the  eruption  just  described  as 
stated  by  Squier,  no  eruption  occurred,  with  the  exci!i)tion 
of  one  on  May  27,  which  followed  the  falling  of  tlmjin^t 
consklerahle  shower  of  rain.  The  fact  that  an  eruption 
followed  the  rain  may  have  been  a  coincidence  simply, 
but  is  suggestive,  in  connection  with  what  is  known 
concerning  the  part  played  by  water  in  volcanic  eruptions. 

In  order  to  bring  the  records  of  the  young  volcanoes  of 
the  North  American  continent  into  one  group,  wo  will 
borrow  from  a  chapter  in  advance,  which  deals  with  the 
volcanic  records  of  Mexico,  an  account  of  the  birth  of 
what  is  now  an  imposing  mountain,  known  as  Jorullo. 

Jorullo,  Mexico. — Jorullo,  frequently  cited  as  a  volcanic 
mountain  that  was  upraised  in  a  single  night,  is  situated 
about  170  miles  westward  of  the  city  of  Mexico.  Its 
fame  is  due  largely  to  the  account  of  its  origin  and  early 
history  given  by  Humboldt,^  who  visited  it  fifty-six  years 
after  its  birth. 

In  spite  of  the  veneration  we  feel  for  the  writings  of 

1  A.  von  Humboldt,  "  Political  Essay  on  the  Kingdom  of  Xew  Spain," 
translated  by  John  Black,  London,  1811,  Vol.  11.  pp.  '211-223.  See  also 
"  Cosmos,"  translated  by  Otte  and  Paul,  Xew  York,  1809,  Vol.  V.  pp.  2!»;5, 
291,  297-301. 


VOLCANOKS    OK   rKNTKAL    AMKKICA 


l.")3 


t\w  immortal  IIumltoMt,  one  is  inolinod.  on  reiulim^  his 
accoiiut  o.  Jorullo,  to  ([iiostion  tlui  autlicntioity  of  tliu  in- 
formation on  which  ho  l)asos  his  very  graphic  description. 
As  stated  by  Ilumholdt,  th(;  acconnt  of  the  remarkable 
occnrrence  referred  to,  was  snni^'  in  hexanu.'ter  verses  by 
the  Jesnit  P'atiier  Raphael  Landivar,  a  native  of  Guate- 
mala, and  also  recorded  by  the  Abl)e  Clavigero,  in  an  an- 
cient history  of  his  country  ("Storia  antica  di  Messico"). 
These  writings,  which  it  does  not  seem  should  be  con- 
sidered as  possessing  scientific  accuracy,  and  the  narratives 
of  persons  who  Avitnessed  the  catastrophe,  gathered  over 
half  a  century  after  its  occurrence,  are  the  sources  of  the 
information  on  which  Humlxjldt's  fref[uently  quoted  de- 
scription of  the  event  are  based.  While  the  main  features 
of  the  eruption  given  below  may  apparently  l)e  taken  as 
approximately  correct,  many  of  the  details  are  apparently 
exaggerated.  The  theory  held  by  Humboldt,  that  volcanic 
craters  are  formed  by  the  npheaval  of  the  earth's  crust, 
"crater  of  elevation,"  possibly  influenced  his  interpretation 
of  the  reports  of  the  eruption  narrated  to  him.  The  ac- 
count of  the  birth  of  Jorullo  given  )jy  Humboldt  in  his  essay 
on  New  Spain,  but  somewhat  abbreviated,  is  as  follows: 

Jorullo,  it  is  said,  was  formed  in  the  night  of  September 
29,  17")0.  Humboldt  and  Bonpland  visited  it  and  gained 
its  summit  in  1803.  The  plaJn  on  which  Jorullo  stands  is 
elevated  750  to  800  metres  above  the  sea  and  is  surrounded 
In'  volcanic  rocks.  For  some  time  previous  to  the  date 
of  the  eruption  just  given,  the  middle  of  the  plain  was 
occupied  by  fields  of  sugar-cane  and  indigo.  These  fields 
belonged  to  the  plantation  of  San  Pedro  de  Jorullo.  In 
the  month  of  June,  1750,  subterranean  noi.ses  of  an  alarm- 
ing nature  were  heard,  accompanied  by  earthquakes,  which 


I  \ 


f  ! 


ir.t 


VOLCANOKS    OK    XOUTII    AMKKKA 


I! 


Hh 


i  i: 


.succcL'dud  OIK'  Jinotlii'i-  for  lifty  or  .sixty  days.  From  tlu^ 
hcgiiuiin.L!;  of  ScjjliMJilx'r,  liowover,  until  tliu  tinic  of  the 
tTuptioii,  tr!iii(|uillity  .st^cMiK^l  rostored,  l)iit  in  IIil'  iii^ht 
Ijctween  SeptendnT  28  and  29,  tlio  subtorraiiuau  noises 
recommenced. 

'•The  at'frightcMl  inhabitants  11(^(1  to  the  mountains  of 
Agnasarco.  A  tract  of  ground  from  three;  to  four  .s(|uare 
miles  ^  in  extent,  which  goes  hy  the  nana;  of  Jfa/jjaj/s, 
ro.se  lip  in  the  sha[)e  of  a  bladder.  The  bounds  of  this 
convulsion  are  still  distinguishalde  in  thefraetural  strata. 
The  MuljKUjs  [answering  to  the  aa  hiva,  surfaces  described 
on  a  previous  page],  near  its  edge,  is  only  twelve  metres 
above  the  old  level  of  the  plain  called  the  jjlat/as  <le 
Jonillo ;  but  the  convexity  of  the  ground  thus  thrown 
up  increases  progressively  towards  the  centre  to  an  ele- 
vation of  160  metres. 

'•  Those  who  witnessed  this  catastrophe  from  the  top 
of  Agnasarco  as.sert  that  flames  were  seen  to  issue  forth 
for  an  extent  of  more  than  half  a  square  league,  that 
fragments  of  burning  rocks  were  thrown  up  to  prodigious 
heights,  and  that  through  a  thick  cloud  of  ashes,  illumi- 
nated by  the  volcanic  fire,  the  softened  surface  of  the 
earth  was  seen  to  swell  up  like  an  agitated  sea.  The 
rivers  of  Cuitamba  and  San  Pedro  [elsewhere  in  the 
narrative  termed  hrooks]  precipitated  themselves  into 
the  burning  chasms.  The  decomposition  of  the  water 
contributed  to  invigorate  the  flames,  which  were  distin- 
guishable at  the  city  of  Pascuaro  [sixty  statute  miles 
distant],  though  situated  on  a  very  extensive  tableland 


t 


ll 


1  The  translator  remarks  in  a  foot-note  tliat  "  the  French  mile  is,  it  is 
believed,  nearly  as  2.887  to  1,  almost  thrice  the  length  of  an  English  mile ; 
but  it  is  uncertain  what  mile  the  author  uses  here." 


Vnl.CANoKS   OK   CKNTIlAL    AMKUKJA 


inf) 


! 


I  H)()  moti't'H  elevated  above  tlie  plains  of  las  jjhii/ns  d, 
Joru/lo.  Ei'iiptions  of  iiiinl,  and  espeeially  of  .strata  of 
(;lay  enveloping  halls  of  deeonii)osed  basalt  in  eoneentri- 
«!al  Inyers,  appeared  fn  indicate  tliat  snbterranean  water 
had  no  small  sliari'  in  piothicini;'  this  extra(M'dinary  revo- 
lution. Tiionsands  of  small  coiuis,  from  two  to  three 
metres  in  heii^ht.  railed  hy  the  indigenes  urciis  {honilfos). 
issued  forth  fnnn  tin?  Ma/jKti/s.   .  .  . 

"In  the  midst  of  the  ovens,  six  ];ii-'j:e  masses,  elevated 
from  400  to  500  metres  each  above  the  old  level  of  the 
plain,  sj)rnng  n}>  from  a  chasm,  of  which  the  direction 
is  from  N.N.E.  to  the  S.S.E.  This  is  the  j)henomenon 
of  the  Montenovo  of  Naples,  .several  times  re[)eated  in 
a  ran^e  of  volcanic  hills.  The  most  elevated  of  these 
enormous  masses,  which  bears  some  resemblance  to  the 
/jifj/s  de  I'Auvergne,  is  the  great  Volcan  de  Jorullo.  It  is 
continually  burning,  and  has  thrown  up  from  the  north 
side  an  innnen.se  (piantity  of  scorified  and  basaltic  lavas 
containing  fragments  of  primitive  rocks.  These  great 
eruj)tions  of  the  central  volcano  continued  till  the  month 
of  February,  1700.  In  the  following  years,  they  became 
gradually  le.ss  frequent.  .  .  .  The  roofs  of  the  houses 
of  Queretaro  were  then  covered  with  a.shes  at  a  distance 
of  more  than  forty -eight  leagues  in  a  straight  line  from 
the  scene  of  the  explosion.  Although  the  subterraneous 
fire  now  appears  far  from  violent,  and  the  Mfifjj(ti/s  and 
the  fjreat  volcano  bei?in  to  be  covered  with  vegetation, 
we  nevertheless  found  the  ambient  air  heated  to  such  a 
degree  by  the  action  of  the  small  ovens  [hornitos],  that 
the  thermometer  at  a  great  distance  from  the  surface 
and  m  the  shade  rose  as  high  as  43°  C."  In  the  bot- 
tom of  the  crater,  temperatures  of  58°  and  60°  C.  were 


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VOLCANOES   OF   NORTH   AMERICA 


i  1 


obtained.  Fissures  from  which  sulphurous  vapors  were 
escaping  were  found  to  have  a  temperature  of  85°  C. 

There  is  much  more  in  the  narrative  of  Humboldt 
n'lating  to  the  new  volcano,  but  I  doubt  its  value 
when  considered  in  the  light  of  modern  science.  Al- 
though the  main  facts  secured  are  seemingly  correct, 
the  student  of  volcanic  phenomena  will,  I  think,  take 
exceptions  to  many  of  the  details  reported  by  priests 
and  Indians,  and  also  to  the  interpretations  of  these 
reports  by  Humboldt. 

The  four  young  volcanoes  described  in  th.e  la.«t  few 
pages  are  of  great  interest  as  showing  the  nature  of  the 
phenomena  that  attend  the  formation  of  new  volcanic 
vents,  n,  however,  we  consider  a  volcano  as  the  sur- 
face manifestation  of  an  opening  or  conduit,  leading 
down  to  a  central  rey-ion  of  intense  heat  in  the  lower 
portion  of  the  earth's  crust,  it  seems  doubtful  if  we 
should  consider  the  examples  cited  as  new  volcanoes  in 
the  strict  meaning  of  the  term.  In  each  case,  the  out- 
break of  steam,  lava,  etc.,  has  been  in  a  volcanic  region 
and  in  the  immediate  vicinity  of  dormant  or  extinct 
craters,  It  would  seem  rather  that  old  passageways 
have  become  closed  and  the  imprisoned  steam  generated 
by  water  coming  in  contact  with  highly  heated  rocks,  or 
the  effects  of  renewed  pressure  on  the  reservoirs  deep 
below  the  surface,  has  led  to  the  opening  of  new  vents 
alon^r  a  line  of  ancient  fracture. 


Older  Volcanoes 

From  the  numerous  and,  for  the  most  part,  popular 
accounts  of  the  volcanoes  of  Central  America  that  have 
been  published,  it  i°  impossiijle  to  select   sufficient  well- 


VOLCANOES   OF   CENTRAL   AMERICxV 


157 


. 


authenticated  data  tu  enable  one  to  conii)ile  an  adequate 
history  of  the  igneous  mountains  of  that  region. 

The  facts  in  hand  show  that  about  thirty  volcanoes 
have  been  more  or  less  active  within  historic  times. 
These  are  indicated  on  the  list  already  presented.  Him- 
dreds  of  craters  that  have  ceased  to  emit  molten  lava, 
scoria,  lapilli,  etc..  still  discharge  steam  and  sulphurous 
vapors,  and  may,  therefore,  be  classed  as  solfataras. 
Throughout  the  volcanic  belt,  hot  springs  are  numerous, 
which  no  doubt,  in  most  instance.^,  owe  their  high  tem- 
perature to  the  heat  of  volcanic  rocks  below  the  surface, 
but  these  have  received  little  scientific  attention.  In 
this  region,  also,  earthquakes  have  been  of  frequent 
occurrence  and,  in  some  instances,  intimately  associated 
with  volcanic  outbursts. 

Among  the  rocks  in  the  volcanic  region  mentioned  by 
travellers  or  described  by  the  few  geologists  who  have 
studied  them,  basalt  is  of  limited  occurrence.  The  moun- 
tains are  composed  principally  of  trachytic  rocks,  and  the 
country  over  large  areas  is  deeply  covered  with  lapilli, 
pumice,  dust,  etc.,  which  record  the  energy  of  explosive 
volcanic  eruptions.  It  is  the  decay  of  these  fragmental 
products  especially,  under  the  influence  of  tropical  rains 
and  a  high  temperature,  that  gives  to  much  of  Central 
America  its  wonderfully  rich  soils. 

Instead  of  attempting  to  assemble  all  the  available  data 
relating  to  the  older  volcanoes  of  Central  America,  I  shall 
select  a  few  of  the  most  typical  examples  of  volcanic 
eruptions  and  of  volcanic  mountains,  not  alone  for  their 
geographical  interest,  but  as  illustrations  of  the  life  his- 
tories of  volcanoes  in  general.  The  examples  chosen  are 
Conseguina,  Fuego,  and  Agua. 


s 

I: 


T 


" 


', 


158 


VOLCANOES    OF    NORTH    AMERICA 


Conseguina.  —  Of  all  the  volcanoes  on  the  Ncjrth  Ameri- 
can continent,  none  have  attracted  a  greater  share  of 
attention  than  Conseguina.  It  is  i)lace(l  first  among  the 
volcanoes  here  especially  considered,  having  '"  by  merit 
been  raised  to  that  bad  eminence,"  on  account  of  its  fear- 
ful eruption  in  1835.  Previous  to  the  explosion  of  Kra- 
katoa  in  1883,  Con.secjuina,  totjether  with  Sunibawa  on  the 


Fir,,  (i.    Sketch  of  Conseguina     (Dollfus  and  Mont-Serrat.) 

island  of  Sumatra,  served  as  the  best  example  of  volcanic 
explosion  on  record. 

Conseguina  is  situated  on  the  Pacitic  coast  of  Nicaragua, 
and  forms  the  principal  elevation  of  a  peninsula  which 
projects  from  the  mainland  towards  the  northwest  and 
partially  shuts  off  the  Bay  of  Fonseca  from  the  sea.  The 
volcano  is  now  extinct  or  dormant.  From  a  distance  it 
presents  the  appearance  of  a  truncated  cone,  with  an  ex- 
treme elevation  above  the  sea  of  a  little  less  than  four 
thousand  feet.      When  more  closelv  examined  the   low 


VOLCANOES   OF   CENTRAL   AMERICA 


150 


mountain  i.s  found  to  contain  a  comparatively  large  crater- 
like depression  in  its  summit. 

Of  the  ap[)earance  of  Conseguina  previous  to  its  now 
historic  eruption  in  18o5,  there  seems  to  be  no  authentic 
record.  At  tiiat  time  the  summit  of  the  mountain,  which 
had  been  formed  l)y  material  ejected  during  previous 
eruptions  of  a  milder  cliaracter,  was  literally  blown  away, 
and  the  rocks  composing  it  reduced  to  fragments  and 
distributed  far  and  wide  over  the  adjacent  sea  and  land. 
By  extending  upward  the  sides  of  the  truncated  cone 
now  remaining,  an  approximate  restoration  of  the  form 
of  the  original  mountain  may  be  made,  which  indicates 
that  its  height  was  in  the  neighborhood  of  8000  or 
10.000  feet.  This  estimate,  however,  would  be  approxi- 
mately correct  only  in  case  the  mountain  had  been  formed 
by  comparatively  mild  explosive  eruptions.  It  may  have 
been  truncated  by  violent  explosions,  previous  to  the  one 
of  which  we  have  a  record. 

The  appearance  of  Conseguina  as  seen  from  the  sea  is 
shown  in  the  accompanying  sketch,  copied  from  Dollfus 
and  Mont-Sorrat.'  The  crater  within  the  truncated  cone 
has  a  diameter  of  four  miles  and  a  depth  below  the  high- 
est point  of  its  rim  of  three  hundred  feet. 

Of  the  many  accounts  of  the  eruption  of  Conseguina 
that  have  been  published,  the  most  graphic  as  well  as  the 
most  accurate,  so  far  as  I  can  judge,  is  one  compiled  by 
Sc|uier,^  about  fifteen  years  after  the  occurrence.  This 
account  reads  as  follows  : 

'  A.  Dollfus  et  E.  de  ^loiit-Serrat,  "Voyage  geologiciue  dans  les  repub- 
liqiies  de  (iiiatemala  et  (if  Salvador,"  Paris,  1808. 

-  E.  G.  Squier.  "On  the  Volcanoes  of  Central  America,"  American  Asso- 
ciation for  the  Advancement  of  Science,  Proceedings,  Xew  Haven  meeting, 
1850,  pp. 107-109. 


1 


'n 


wsmm 


1(]0 


VOLCANOES   OF   NOUTH   AMERICA 


!''!'• 


■:f 


*   '     I 

!•     i- 


'•  On  the  morning  of  the  20tli  of  Janiuiry  in  that  year 
[1835],  several  loud  explosions  were  heard  for  a  radius  of 
a  hundred  leagues  around  this  volcano,  followed  by  the 
rising  of  an  inky  black  cloud  above  it,  through  which 
darted  ton<jjues  of  flame  resembling  lightning.  This  cloud 
gradually  spread  outward,  obscuring  the  sun,  and  shed- 
ding over  everything  a  yellow,  sickly  light,  and  at  the 
same  time  depositing  a  fine  sand,  which  rendered  respira- 
tion difficult  and  painful.  This  continued  for  two  days, 
the  obscuration  becoming  more  and  more  dense,  the  sand 
falling  niijre  thickly,  and  tlie  explosions  becoming  louder 
and  more  frequent.  On  the  third  day,  the  explosions 
attained  their  maximum,  and  the  darkness  became  intense. 
Sand  continued  to  fall,  and  the  people  deserted  their 
houses,  fearing  the  roofs  might  yield  beneath  the  weight. 
This  sand  fell  several  inches  deep  at  Leon,  more  than  one 
hundred  miles  distant.  It  fell  in  Jamaica,  Vera  Cruz,  and 
Santa  Fe  de  Bogota,  over  an  area  of  1500  miles  in  diame- 
ter. The  noise  of  the  explosions  was  heard  nearly  as  far, 
and  the  Superintendent  of  Belize,  eight  hundred  miles 
distant,  mustered  his  troops,  under  the  impression  that 
there  was  a  naval  action  off  the  harbor.  All  nature 
seemed  overawed  ;  the  birds  deserted  the  air,  and  the 
wild  beasts  their  fastnesses,  crouching,  terror-stricken  and 
harmless,  in  the  dwellings  of  men.  The  people  for  a 
hundred  leagues  grouped,  dumb  with  horror,  amidst  the 
thick  darkness,  bearing  crosses  on  their  shoulders  and 
stones  on  their  heads,  in  penitential  abasement  and  dis- 
may. Many  believed  the  day  of  doom  had  come,  and 
crowded  to  the  tottering  churches,  where,  in  the  pauses 
of  the  explosions,  the  voices  of  the  priests  were  heard  in 
solemn  invocation  to  Heaven.     The  Ijrightest  lights  were 


VOLCANOES   OF   CENTRAL   AMETlICA 


161 


iir, 
iiiles 
hat 
lire 
the 
and 
Dr   a 
the 
and 
dis- 
and 
uses 
in 
were 


invisible  at  the  distance  of  a  few  feet ;  and  to  heighten 
the  terror  of  the  scene,  occasional  lightnings  traversed 
the  darkness,  shedding  a  lurid  glare  over  the  eafth.  This 
continued  for  forty-three  hours,  and  then  gradually  passed 
away. 

"  For  some  leagues  around  the  volcano,  the  sand  and 
ashes  had  fallen  to  a  depth  of  several  feet.  Of  course, 
the  operations  of  the  volcano  could  only  be  known  by  the 
results.  A  crater  had  been  opened,  several  miles  in  cir- 
cumference [about  twelve  miles,  according  to  Dullfus  and 
Mont-Serrat],  from  which  had  flowed  vast  quantities  of 
lava  into  the  sea  on  one  hand,  and  the  Gulf  of  Fonseca 
on  the  other.  The  verdant  sides  of  the  mountain  were 
now  rough,  burned,  and  seamed,  and  covered  with  dis- 
rupted rocks  and  fields  of  lava.  The  quantity  of  matter 
ejected  was  incredible  in  amount.  I  am  informed  by  the 
captain  of  a  vessel  which  passed  along  the  coast  a  few 
days  thereafter,  that  the  sea  for  fifty  leagues  was  covered 
with  floating  masses  of  pumice,  and  that  he  sailed  for  a 
whole  day  through  it  without  being  able  to  distinguish, 
except  here  and  there,  an  open  space  of  water. 

"  The  appearance  of  this  mountain  is  now  desolate  be- 
yond description.  Not  a  trace  of  life  appears  upon  its 
parched  sides.  Here  and  there  are  openings  emitting 
steam,  small  jets  of  smoke,  and  sulphurous  vapors,  and  in 
some  places  the  ground  is  swampy  from  thermal  springs. 
It  is  said  that  the  discharge  of  ashes,  sand,  and  lava  was 
followed  by  a  flow  of  water,  and  the  story  seems  corrobo- 
rated by  the  particular  smoothness  of  some  parts  of  the 
slope." 

The  terror  inspired  in  the  minds  of  the  people  inhabit- 
ing the  region  about  Conseguina  calls  to  mind  the  graphic 


ni 


■  *^  .^-wmtx-^mmf^ 


162 


VOLCANOES    OF   NORTH    AMEIUCA 


I 


* 


( .    • 


i: 


ri; 


picture  of  tlio  destruction  of  Pompeii  rluring  an  eruption 
of  Vesuvius,  given  by  Bulwer.  Tlie  eruptions  in  each 
instance  were  of  a  similar  character,  the  summit  of  a 
mountain  in  each  case  l)eing  blown  to  fragments. 

The  explosion  as  witnessed  at  the  town  of  La  Union  on 
tlie  nortliwest  shore  of  the  Bay  of  Fonseca,  about  forty 
miles  distant  from  Conseguina,  has  been  described  by  Lieu- 
tenant Colonel  C.  Manuel  Romero,*  commandant  of  the 
post,  from  whose  account  the  following  has  been  compiled  : 

The  dawn  of  the  day  on  which  the  eruption  began  (Jan- 
uary 20,  1835)  was  serene,  bu'o  at  eight  o'clock  a  dense 
black  cloud  was  seen  rising  toward  the  southeast,  pre- 
ceded by  a  rumbling  noise.  The  cloud  continued  to 
ascend  until  about  ten  o'clock;  when  it  covered  the  sun 
and  then  began  to  spread  toward  the  north  and  south ;  it 
continued  to  spread  until  it  covered  the  whole  firmament, 
and  at  about  eleven  o'clock  enveloped  everything  in  the 
greatest  darkness.  The  darkness  was  so  intense  that  the 
nearest  objects  were  imperceptible.  During  this  spreading 
of  the  cloud  it  was  rent  by  lightning  flashes,  accompanied 
by  thunder.  At  four  in  the  afternoon,  the  earth  began  to 
quake,  and  continued  in  a  perpetual  undulation,  which 
gradually  increased  in  force.  Next  came  a  shower  of  what 
is  stated  to  have  been  "  phosphoric  sand,"  which  lasted 
until  eight  in  the  evening,  when  a  fine,  heavy  powder  like 
flour  began  falling.  Lightning  and  thunder  continued  the 
whole  night,  and  the  following  day  (January  21)  at  eight 
minutes  past  three  in  the  afternoon,  an  earthquake  shock 
of  such  violence  occurred  that  men  were  thrown  down. 


*  Reprinted  from  "Boletin  oficial  del  Estado  de  Guatemala,"  1835,  by 
Dollf  us  and  Mont-Serrat,  p.  334.  A  translation  by  Colonel  Juan  Galindo 
maybe  found  in  the  American  Journal  of  Science,  Vol.  28, 1835,  pp.  332-334. 


i; 


VOLCANOES   OF   CENTRAL   AMEKICA 


1G3 


ilgllt 


|35,  by 
lalindo 
I2-334. 


The  effects  of  the  appalling  scene  on  men  and  beasts 
were  also  noted.  The  darkness  lasted  fur  forty-three 
hours.  On  tlie  22d,  it  was  less  dark,  although  the  sun 
was  still  invisible,  and  towards  morning  on  tlie  23d,  tre- 
mendously loud  thunder  ('la})s  were  heard  in  succession, 
like  the  firing  of  the  heaviest  of  artillery.  This  fresh 
occurrence  was  followed  by  an  increase  in  the  dust  shower. 

On  the  25th^  2Gtli,  and  27tli,  there  were  frequent,  al- 
though not  violent,  earthquake  shocks.  The  showers  of 
dust  Listed  until  the  27th.  Galindo  mentions  other  erup- 
tions that  occurred  at  the  same  time  with  the  outburst  of 
Conseguina,  five  of  which  continued  for  eight  days.  In 
conclusion  he  says  :  '•  The  volcanic  energy  seems  to  have 
operated  on  an  extensive  scale,  and  to  have  had  vent  in  a 
great  number  of  places.  The  country  from  Bogota,  about 
latitude  4°  30'  N.,  longitude  74°  14'  W.,  throughout  the 
whole  isthmus,  certainly  as  far  as  Belize  [more  than  1000 
miles  from  the  centre  of  disturbance]  was  convulsed,  or 
affected  by  the  concussions." 

Following  the  great  explosion  just  described  came  fear- 
ful earthquakes  along  the  Andes.  The  most  disastrous  of 
these  was  on  February  20tli,  but  they  continued  at  the 
rate  of  three  or  four  a  day  up  to  March  6th,  and  less  fre- 
quently to  March  17th.  During  one  of  these  earthquakes, 
the  city  of  Conception,  Chile,  with  a  population  of  2o,000, 
was  destroyed,  only  a  single  house  remaining  standing. 

After  the  eruption  of  Conseguina,  brilliant  sunsets  and 
sunrises,  due  to  the  quantity  of  fine  particles  blown  high 
in  the  air  and  drifted  by  the  wind  to  distant  regions,  were 
observed  at  widely  separated  localities. 

The  great  eruption  of  Conseguina,  1835,  just  described, 
presented  in  many  ways  the  phenomena  that  accompanied 


li 


I.  If 


164 


VOLCANOES  OF   NORTH   AMERICA 


i 


i 


the  explosion  of  Krakatoa  in  1883.  The  latter  eruption 
was  more  carefully  studied  and  a  far  better  report  made 
concerning  it  than  in  the  case  of  the  former.  A  better 
conception  of  what  took  place  at  the  explosion  of  Conse- 
guina  can  be  gathered  from  reading  the  accomit  of  the 
eruption  of  Krakatoa  given  on  a  previous  page,  in  con- 
nection with  the  reports  just  cited,  than  can  be  had  from 
the  imperfect  and  unscientific  accounts  which  are  alone 
available  concerning  the  occurrence. 

As  will  be  seen  when  the  theories  advanced  to  explain 
volcanic  eruptions  are  considered,  the  violent  explosions 
that  shook  Central  America  at  the  time  the  summit  of 
Conseguina  was  blown  away,  were  caused  by  an  escape  of 
steam  augmented  perhaps  by  the  ignition  of  gases.  A 
large  volume  of  water  probably  gained  access  to  the  liquid 
lava  that  rose  in  the  conduit  of  the  volcano,  and  the  steam 
and  gases  generated  blew  the  liquid  lava  and  the  enclos- 
ing rocks  to  fragments  and  showered  them  over  the 
surrounding  region. 

Volcan  del  Fuego.  —  Since  the  Spanish  conquest  about 
fifty  volcanic  eruptions  have  been  chronicled  in  Central 
America.  Of  these,  twenty  are  accredited  to  Fuego.  This 
unusually  energetic  volcano  was  in  full  activity  at  the 
time  of  the  Spani.sh  invasion,  but  became  less  and  less 
demonstrative  during  the  sixteenth  and  seventeenth  cen- 
turies, and  for  many  years  has  been  in  the  solfataric 
stage.  The  recent  quiescence  is  to  be  regarded  with  sus- 
picion, however,  since,  like  many  other  volcanoes  of  Cen- 
tral America,  Fuego  is  of  the  Vesuvian  type.  A  period  of 
rest  may  mean  that  the  lava  in  the  upper  part  of  its 
conduit  is  slowly  cooling  and  hardening,  so  as  to  confine 
the  steam  generated  beneath,  which  will  finally  gain  such 


VOLCANOES   OP  CENTRAL   AMEUICA 


165 


bout 
itral 
This 
the 
less 
cen- 
taric 
sus- 
Cen- 
dof 
If  its 
In  fine 
such 


energy  as  to  again  open  a  passage  to  tlio  surface.  When 
this  occurs,  the  history  of  Vesuvius  in  7'J,  or  of  Conseguina 
in  1835,  may  be  repeated. 

Fuego,  Agua,  Acatenango  tlie  highest  suniniit  in  Cen- 
tral America,  and  a  number  of  snuilh'r  volcanoes,  form 
a  secondary  group  trending  approximately  north  and 
south,  and  nearly  at  right  angles  to  the  main  vcjlcanic 
belt.  All  of  the  craters  in  this  group,  except  Fuego,  are 
extinct  or  have  long  since  passed  to  the  solfataric  stage. 

The  volcano  of  Fuego  and  its  higher  neighbor,  Acate- 
nango, called  also  Pico  Mayor  and  Padre  del  Volcan,  are 
united  up  to  an  elevation  of  3000  metres,  but  above  that 
elevation  rise  as  independent  cones.  Fiiego  is  a  perfectly 
regular  cone  of  lapilli  with  surface  slopes  of  28°  to  32^^, 
on  all  sidc»s,  except  the  north,  where  a  prominent  shoulder 
330  metres  below  its  summit,  termed  la  Meseta,  gives 
it  an  exceptional  profile.  This  table-like  projection  is 
a  remnant  of  a  vast  truncated  cone,  the  summit  of 
which  was  blown  away  in  prehistoric  times,  and  bears 
a  similar  relation  to  the  modern  cone  towering  above  it, 
that  Sonmia  does  to  Vesuvius. 

Regarding  the  past  activity  of  Fuego,  Dollfus  and 
Mont-Serrat^  state  that  it  had  probably  been  in  activity 
for  a  long  time  previous  to  the  Spanish  invasion  of  Gua- 
temala, as  the  natives  at  that  time  lield  it  in  dread. 
During  the  following  centuries  its  eruptions  were  fre- 
quent and  terrible.  It  occupied  a  leading  place  among 
the  many  active  volcanoes  which  at  the  time  referred  to 
were  covering  Central  America  with  lava  and  storms  of 
cinders  and  lapilli. 

1  A.  Dollfus  et  E.  de  Mont-Serrat,  "Voyage  geologique  dans  les  republiques 
de  Guatemala  et  de  Salvador,"  Paris,  1888. 


mmrwm 


I      V 


; 


ri 


luo 


VOLCANOES   OF    NOUTH    AMKUICA 


AiiK-mg  tlio  iiioro  violent  oruptionH  arc  citocl  those  of 
1520,  1541,  the  27th  of  December,  1581,  wlieu  the  quan- 
tity of  lapilli  and  (hist  projected  into  the  atinospliere  was 
so  great  tliat  the  sun  was  completely  ol)Scured,  and  lamps 
were  lighted  at  midday  at  La  Antigua,  fifteen  kilometres 
distant.  During  1582,  1585,  and  158G  there  were  erup- 
tions almost  every  month ;  the  most  terrible  being  on 
December  23,  1580.  Memorable  eruptions  occurred  also 
in  1014,  1023,  1080,  1705,  1700.  On  August  27  and  28, 
1717,  explosions  covered  the  surrounding  country  with 
cinders  ;  accompanying  this  eruption  violent  subterranean 
detonations  are  recorded.  Other  eruptions  occurred  in 
1732,  1739, 1829,  and  1855.  On  January  9,  1850,  cinders 
were  shot  into  the  air,  with  such  violence  that  they  fell 
at  Tocoy,  150  kilometres  to  the  northward  ;  it  is  remarked 
that  the.se  cinders  contained  ten  per  cent  of  magnetic 
iron.  The  volcano  was  again  in  eruption  on  February  17, 
1857.  Finally,  on  August  17,  1800,  there  was  a  small 
eruption,  but  since  that  date  to  1800  (and  I  believe  to 
the  present  time,  1890)  this  remarkable  volcano  has  been 
([uiet,  although  there  is  always  a  cloud  of  steam  above  its 
summit. 

The  numerous  eruptions  recorded  were  nearly  all  of  the 
explosive  type  ;  the  material  ejected  being  usually  scoria, 
cinders,  lapilli,  ai  d  blackish  or  violet  colored  volcanic 
sand.  No  great  effusions  of  lava  are  mentioned,  but  a 
few  small  flows  have  occurred  from  fissures  near  the  base 
of  the  cone.  No  molten  lava  is  known  to  have  been 
erupted  from  the  summit. 

Dollfus  and  Mont-Serrat  ascended  Fuego  in  May,  1800. 
After  traversing  the  dense  tropical  forests  on  the  lower 
slopes  of  the  mountain,  the  region  of  pines  was  reached 


^n 


I 


I  i 


VOLCANOES   UV   ClCNTUAI.    AMKllICA 


167 


;6. 


at  an  elevation  of  about  3UUU  nietios.  A  little  below 
la  Maseta  the  pines  gave  i)lace  to  grass-covered  slopes,  but 
this  is  not  tiie  true  '•  tinibctr  line."  Tiie  forcists  cease  be- 
cause the  lapilli  of  which  the  ground  is  composed  has  not 
decayed  sullicicntly  to  form  a  soil.  Un  neighboring  i)eaks 
the  forest  reaches  an  elevation  of  4000  metres,  and  even 
the  highest  summits  when  soil  is  present  are  grass  covered. 

At  the  summit  there  is  an  irregular  crater  fifty  metres 
wide  and  twenty-five  metres  (lee[),  lloored  with  lapilli,  in 
the  walls  and  bottom  of  which  there  are  several  fumaroles. 
This  crater  has  evidently  been  inactive  for  some  time,  but, 
at  a  little  lower  level  to  the  southwest,  there  is  a  gigantic 
cavity,  partially  defacing  its  rim,  from  which  inunense 
volumes  of  vapor  pour  out.  This  active  crater  is  almost 
circular,  with  a  diameter  of  300  or  400  metres,  and  a 
depth  of  600  metres.  The  bottom  is  of  scoria,  although 
it  must  have  been  an  open  conduit  at  the  time  of  the 
eruption  of  1860.  The  walls  of  the  crater  are  nearly 
vertical,  and  highest  on  the  northern  side  adjacent  to  ilie 
small  summit  crater. 

The  rim  of  the  great  crater,  in  common  with  nearly 
the  entire  surface  of  the  mountain,  is  composed  of  black, 
brown,  and  red  scoria,  and  lapilli,  the  larger  fragments 
being  about  the  size  of  one's  fist.  The  outer  slopes  of  the 
cone  near  the  top,  as  well  as  the  inner  edges  of  the  crater, 
are  covered  over  large  areas  with  white  and  yellow  in- 
crustations, deposited  from  the  exhalations  of  numerous 
fumaroles.  Both  within  the  craters  and  on  the  adjacent 
outer  slopes  there  are  many  localities  where  steam  and 
gases  escape,  and  join  the  vapors  rising  from  within  the 
main  crater.  The  temperature  of  these  fumaroles  ranges 
from  79°  to  110°.     As   previously  noted  at  Izalco,  the 


168 


VQi:(CANOES   OF   NORTH   AMERICA 


I! 


:  I 


11 


i 


fumaroles  with  lev;  temperatures  give  out  steam  mingled 
with  small  arnoiuits  of  hydrochloric,  sulphuric,  and  car- 
bonic acids,  etc.,  while  from  those  with  higher  tempera- 
tures a  decrease  in  the  volume  of  steam,  accompanied  by 
an  increase  of  gases,  was  noted. 

In  conclusion,  Dollfus  and  Mont-Serrat  state  that  in 
spite  of  the  important  role  that  Fuego  has  already  played, 
it  will  not  soon  be  stricken  from  the  list  of  the  active 
volcanoes  of  Central  America. 

Volcan  de  Agua.  —  It  is  instructive  to  turn  from  the  still 
active  craters  of  Central  America,  and  note  the  condition 
of  those  which  have  long  been  extinct.  Perhaps  the  most 
interesting  example  of  this  nature  is  furnished  by  Volcan 
de  Agua,  situated  in  Guatemala,  and  a  near  neighbor  of 
the  extremely  active  Volcan  del  Fuego,  of  which  a  short 
account  has  just  been  given,  and  of  the  ancient  and  now 
much  weathered  volcanic  peak,  known  as  Pacaya. 

The  account  of  Agua  here  presented  is  taken  almost 
wholly  from  the  great  work  of  Dollfus  and  Mont-Serrat, 
already  referred  to.  These  authors  state  that  the  scene 
which  the  traveller  beholds  from  the  summit  of  Pacaya  is 
one  of  the  most  imposing  imaginable.  One  sees  in  a 
single  glance,  grouped  as  in  a  picture,  the  grand  out- 
lines of  Fuego,  and  in  the  foreground  the  harmonious, 
gently  curving  lines  leading  to  the  tapering  summit  of 
Agua.  The  beauty  of  the  scene  is  due  in  a  great  measure 
to  a  slight  irregularity  which,  without  affecting  the  sym- 
metry of  the  grouping  of  the  peaks,  brings  Agua  one  or 
two  kilometres  north  of  the  general  direction  of  the  other 
elevations,  and  so  permits  the  eye  to  sweep  over  a  great 
expanse  without  interruption. 

Considered  by  itself  Agua  is  one  of  the  most  remarkable 


VOLCANOES   OF   CENTllAL   AMERICA 


169 


of 


volcanic  mountains  in  Central  America.  Its  beauty  is  due 
not  only  to  its  considerable  height  and  the  luxuriousness 
of  the  forests  about  its  base  and  clothing  its  lower  slopes, 
but,  in  a  great  measure,  to  its  isolation.  It  rises  as  a 
single  cone  to  an  elevation  of  3753  metres  al)ove  the  sea. 
Its  immediate  base  covers  an  area  of  several  hundred 
square  kilometres.  To  the  north  its  lower  slope  merges 
with  the  spurs  of  a  mountain  known  as  Santa  Maria,  but 
to  the  south  its  visual  height  is  almost  3500  metres.  To 
the  east  and  west  it  is  separated  from  Pacaya  and  Fucgo 
^y  valleys  which  it  overtops  by  more  than  2000  metres. 
Its  isolation  is  thus  complete.  Having  been  extinct  for  a 
long  time,  its  surface  is  broken  by  stream  channels,  but 
these  irregularities  are  slight,  and  disappear  when  the 
mountain  is  viewed  from  a  distance. 

Vegetation  has  completely  covered  the  great  cone,  and, 
thanks  to  its  isolation,  the  normal  distribution  of  plant 
life  according  to  climatic  belts  is  clearly  marked.  A 
series  of  well-defined  plaiit  zones  can  be  seen  surrounding 
the  cone,  which  play  an  important  part  in  beautifying  it, 
and  in  imparting  to  it  a  harmonious  variety  of  colors. 
Cultivated  fields  surround  the  base  of  the  mountain,  and 
extend  up  its  sides  to  an  elevation  of  2580  metres.  In 
ascending,  one  passes  in  upward  succession  productive 
fields  of  sugar-cane,  coffee,  and  maize ;  then  comes  a 
splendid  forest  of  various  kinds  of  trees,  including  a  num- 
ber of  tropical  species.  This  forest  continues  to  a  height 
of  3027  metres,  and  then  gives  place  abruptly  to  vast 
open  spaces  with  sparsely  growing  pines,  between  which 
are  luxuriant  shrubs  and  flowers  of  species  unknown  in  the 
lower  region.  The  extreme  summit  and  the  floor  of  the 
crater  v>rhicli  there  exists,  are  grass  covered. 


170 


VOLCANOES   OF   NORTH   AMERICA 


/: 


IT  I*     •: 


I'       I 


The  name  of  this  charming  mountain,  Volcan  de  Agua, 
or  water  volcano,  has  led  some  persons  to  suppose  that  it 
is  a  volcano  which  erupts  water ;  while  others  state  that 
snow  on  its  sides  is  sometimes  melted  by  the  heat  from 
within,  and  descends  in  floods  into  the  neighboring  valleys. 
We  are  assured  by  Dollfus  and  Mont-Serrat,  however,  that 
neither  of  these  explanations  is  correct.  The  origin  of  the 
name  is  this :  at  the  time  of  the  Spanish  invasion,  the 
crater  at  the  summit  of  the  mountain  contained  a  lake, 
which  was  supplied  by  rain.  In  1541,  as  the  result  of  an 
earthquake,  the  wall  of  the  crater  on  the  northeastern 
side  gave  way,  and  an  immense  volume  of  water  poured 
down  the  mountain  side,  carrying  with  it  earth,  rocks,  and 
trees  that  obstructed  its  course,  and  overwhelmed  a  village 
which  had  been  built  by  the  Spaniards  on  the  site  where 
to-day  stands  the  town  of  Ciudad  Vieja. 

The  present  condition  of  the  mountain  confirms  this 
account,  which  Las  been  derived  from  historical  records. 
The  crater  presents  all  the  characteristics  of  a  former  lake 
basin,  and  upon  the  side  of  the  mountain  an  immense 
ravine  can  be  clearly  seen,  departing  from  a  place  where 
the  rim  of  the  crater  is  broken,  and  extending  in  the 
direction  of  Ciudad  Vieja. 

The  soil  of  the  valleys  near  the  base  of  Agua  is  de- 
scribed in  the  book  we  are  citing,  as  being  composed  of 
layers  of  white  pumice,  yellowish  cinders,  black  lapilli, 
and  violet  sands.  No  traces  of  lava  flows  were  found. 
On  the  lower  slope  of  the  cone,  where  the  ground  has  an 
inclination  of  from  28°  to  30°,  the  fertile  soil  contains 
pumice  and  scoria,  with  a  good  proportion  of  yellow  clay. 
At  an  elevation  of  2664  metres,  in  an  opening  cleared  in 
the  dense  forest,  the  soil  was  found  to  consist  of  a  thick 


VOLCANOES   OF   CENTRAL   AMERICA 


171 


layer  of  decayed  volcanic  sands  and  black  lapilli  in  small 
fragments.  The  vast  abundance  of  material  such  as  is 
ejected  during  explosive  eruptions,  and  the  absence  of  lava 
flows,  as  well  as  the  character  of  the  crater  walls,  which 
are  also  of  fragmental  products,  show  that  Agua,  during 
its  days  of  activity,  was  a  volcano  of  the  explosive  type. 
Its  perfection  of  form  is  no  doubt  due  to  its  having  been 
built  by  the  accumulation  of  projectiles  shot  into  the  air, 
and  falling  about  their  place  of  egress.  The  eruptions 
were  probably  never  sufficiently  violent  to  blow  away  the 
summit  of  the  cone,  and,  so  far  as  known,  no  breaks  in  its 
sides  led  to  the  formation  of  dikes.  Its  grace  and  sym- 
metry indicate  that  it  was  built  up  by  long-continued  but 
comparatively  mild,  explosive  eruptions. 


CHAPTER  IV 


i: 


VOLCANOES  OF  iMEXICO 

The  distribution  of  the  better  known  volcanoes  of  Mexico  ia  shown  on  Plate  4. 

Humboldt  states  that  the  only  volcanoes  m  Mexico 
that  have  been  active  within  historic  times  are  Tuxtla, 
Popocatepetl,  Jorullo,  and  Colima,  but  this  list  has  been 
somewhat  extended  since  he  wrote.  The  geology  of  Mex- 
ico is  still  but  imperfectly  known.  Travellers  report  many 
craters  and  mountains  besides  those  just  mentioned,  that 
are  of  recent  date,  and  also  extensive  lava  fields  and  vast 
deposits  of  lapilli  and  volcanic  dust,  which  are  the  last 
additions  made  to  the  soil  over  broad  regions. 

The  narrow  belt  of  fractures  and  faults,  with  their  ac- 
companying volcanic  phenomena,  which  is  such  a  pro- 
nounced feature  in  the  geology  and  geography  of  Central 
America,  is  continued  into  Mexico  with  a  marked  increase 
in  breadth.  In  south-central  Mexico  the  volcanic  belt 
broadens  until  it  touches  both  the  Gulf  and  Pacific  coasts. 
Accompanying  this  increase  in  width  is  a  decrease  in  the 
number  of  active  craters,  and  a  diminution  in  their  inten- 
sity. All  of  the  still  active  volcanoes  are  confined  to  the 
region  south  of  latitude  22°;  that  is,  they  are  situated 
south  of  an  east  and  west  line,  crossing  the  Republic 
about  200  miles  north  of  the  city  of  Mexico. 

The  best  accounts  of  the  physical  geography  of  Mexico 
that  have  come  under  my  notice,  are  in  the  well-known 

172 


T 
\ 


fF 


VOLCANOES   OF   MEXICO 


173 


writings  of  Humboldt,  and  in  the  recently  published  vol- 
ume entitled  •'  North  America,"  by  Reclus.'  Descriptions 
of  Mexican  volcanoes,  in  most  instances  of  a  popular  char- 
acter, have  been  given  by  numerous  travellers  and  by 
Spanish  priests.  In  a  few  instances  definite  and  reliable 
observations  have  been  made  by  members  of  scientific  ex- 
peditions ;  among  these,  the  ones  that  have  been  found  of 
most  assistance  are  those  published  by  the  Geological  Sur- 
vey of  Mexico.  From  this  varied  store  of  information,  I 
have  selected  such  facts  as  will  assist  the  student  in  grasp- 
ing the  leading  characteristics  of  volcanoes  in  general, 
and,  at  the  same  time,  furnish  information  concerning  the 
physical  geography  and  geology  of  Mexico. 

Orizaba.  —  This  reuiarkably  regular  and  beautiful  sym- 
metrical mountain  is  situated  in  the  eastern  part  of  Mex- 
ico, and  a  little  south  of  a  straight  line  joining  the  city 
of  Mexico  and  Vera  Cruz.  It  is  about  seventy-five  miles 
west  of  Vera  Cruz,  and  in  sight  from  that  city.  Orizaba 
derives  its  present  name  from  the  city  of  Orizaba,  near 
which  it  rises,  and  is  known  also  by  its  ancient  Aztec 
name,  Citlal-tepetl,  or  Star  Mountain.  Its  elevation  is 
approximately  18,200  feet.  For  a  time  it  was  consid- 
ered the  highest  summit  in  North  America,  but  is  now 
known  to  be  surpassed  in  elevation  by  Mt.  Logan  (19,500), 
situated  in  northwestern  Canada,  near  the  Alaskan  bound- 
ary. Triangulations  made  by  Ferrer  in  1796  placed  the 
height  of  Orizaba  at  17,879  feet.  Humboldt,  by  similar 
methods,  but,  as  he  states,  under  unfavorable  conditions, 
found  it  to  be   17,375  feet.-    Recent   measm^ements   by 


1  filisee   Reclus,   "  The  Earth  and  its  Inhabitants :  North  America." 
Edited  by  A.  H.  Keane,  New  York,  1891,  Vol.  II. 

2  "  Cosmos,"  New  York,  1869,  Vol.  V,  p.  239. 


\\:   \ 


f 
t 


I! 


ii 


! 


174 


VOLCANOES  OF   NORTH   AMERICA 


means  of  an  aneroid  barometer,  gave  an  elevation  of 
18,205  teet.^ 

Orizaba  rises  from  a  forested  region  and  reaches  the 
lower  limit  of  perpetual  snow,  but  no  glaciers  have  been 
reported  to  occur  about  its  summit.  The  upper  limit  of 
forest  growth,  or  the  "  timber  line,"  is  at  an  elevation  of 
about  12,000  feet.  Above  that  elevation  the  rocks  are 
bare  until  the  snow  that  usually  covers  the  summit  is 
reached. 

At  the  summit,  there  are  three  craters,  separated  one 
from  another  by  ridges  of  lapilli.  The  shapes  of  these 
depressions  show  that  but  little  erosion  has  taken  place 
since  the  eruptions  that  gave  them  their  forms.  The  last 
observed  eruption  is  stated  to  have  occurred  near  the  mid- 
dle of  the  eighteenth  century.  The  igneous  energy  that 
built  the  mountain  is  now  extinct  or  dormant,  and  the 
craters  are  normally  occupied  by  snow.  Like  Mt.  Etna, 
and  many  other  isolated  volcanic  mountains,  Orizaba  is 
surrounded  by  eruptive  rocks,  and  its  flanks  studded  with 
numerous  cinder  cones  and  craters  of  small  size.  Much 
of  the  lava  surrounding  it  came  from  its  own  eruptions, 
and  some  of  the  secondary  cones  are  evidently  parasitic ; 

*  The  elevations  of  four  of  the  higher  volcanic  mountains  of  Mexico  were 
measured  by  Professor  Angelo  Heilprin  in  1889  (Philadelphia  Acad.  Nat.  Sci., 
Proc,  1890,  pp.  251-2G5)  by  means  of  an  aneroid  barometer,  and  the  following 
results  obtained : 

Elevation  of  Orizaba,  18,205  feet  above  the  sea. 

"  Popocatepetl,  17,523     "        "       "      « 

"  Ixtaccihuatl,  16,960    "        «       "      « 

"  Nevado  de  Toluca,  14,954     "        "       "      " 

These  results  differ  considerably  in  each  instance  from  previous  measure- 
ments, and,  on  account  of  the  method  employed,  cannot,  in  the  opinion  of 
men  well  qualified  to  judge  of  such  matters,  be  considered  as  more  than 
approximately  accurate.  The  possible  error  in  each  case  may  be  as  great  as 
five  hundred  feet. 


VOLCANOES   OF   MEXICO 


175 


that  is,  they  owe  their  origin  to  tlie  escape  of  steam  from 
the  lava  flows  on  which  they  are  located,  and  do  not  indi- 
cate the  presence  of  vents  connected  with  conduits  leading 
to  deeply  seated  regions  of  heated  rocks.  Other  crater 
and  lava  flows  apparently  owe  their  origin  to  the  opening 
of  fissures  in  the  sides  of  the  mountain,  which  ucave  e^rress 
to  lava  and  steam  derived  from  the  main  conduit  of  the 
volcano. 

The  summit  of  Orizaba  was  first  reached  by  Reynolds 
and  Maynard,  who  were  connected  with  the  army  of  the 
United  States  which  invaded  Mexico  in  1848.  Since  that 
time  several  ascents  have  been  made.  One  of  the  latest 
of  these  was  by  an  expedition  sent  out  by  the  Academy  of 
Natural  Science  of  Philadelphia,  in  1889,  in  charge  of 
Heilprin.  From  an  account  of  this  ascent  the  following 
notes  have  been  taken  :  ^ 

The  starting-point  for  the  ascent  was  San  Andres,  a 
railroad  town  about  midway  between  the  city  of  Mexico 
and  Vera  Cruz.  San  Andres  has  an  elevation  of  about 
8200  feet.  About  the  town  there  is  a  desert  of  sand, 
scantily  clothed  with  aloes,  cactuses,  and  yuccas,  with  here 
and  there  a  cherry,  oak,  and  an  apple  tree.  To  the  east- 
ward of  San  Andres,  and  barely  twenty-five  miles  distant, 
rises  the  truncated  cone  of  Orizaba,  and  its  twin  neighbor 
Sierra  Negra ;  to  the  west  and  south  are  numerous  vol- 
canic cones,  with  elevations  varying  from  300  to  500  feet 
above  the  arid  lands  surrounding  their  bases. 

At  an  elevation  of  about  1000  feet  above  San  Andres, 
the  exploring  party  left  the  dreary,  open  country  with  its 


*  Angelo  Heilprin,  "  Among  the  World's  Highest  Mountains  :  an  Ascent 
of  Orizaba,  Mexico."  In  "  Around  the  World  "  (a  magazine  published  in 
Philadelphia),  Vol.  1,  1894,  pp.  21-:^6,  49-53,  with  illustrations. 


176 


VOLCANOES    OF    NOllTII    AMERICA 


■I  I  I 


" 


t 


r 


\  ;l 


li 


! 


defert  vegetation,  and  entered  a  region  of  pines.  The 
species  of  pine  that  is  most  ahundant  in  the  lower  portion 
of  the  forest  belt  is  the  long-leaved  T'lnus  Montezuma 
(var.  macrojjJu/Ua).  This  tree  is  found,  seemingly,  on  the 
slopes  of  all  the  giant  volcanoes  of  the  Repul)lic,  asso- 
ciated more  or  less  Avith  a  closely  related  form,  the  Pinus 
psemlostrohiis,  and  with  Phms  Teocote.  The  Montezuma 
pine  grows  also  in  the  neighborhood  of  the  town  of 
Orizaba,  at  an  elevation  of  4500  feet ;  and  on  the  south- 
west slope  of  the  volcano  of  Jorullo,  where  it  descends  to 
4000  feet.  It  flourishes  side  by  side  with  the  palmetto  in 
the  transition  zone  which  unites  the  vegetation  of  the 
lowlands  with  that  of  the  uplands.  This  pine  is  of  stately 
presence.  Its  shaft  is  frequently  a  hundred  feet  or  more 
in  height,  and  grows  in  open  ranks  with  little  or  no  under- 
growth. On  the  lower  slopes  of  Orizaba,  Heilprin  says : 
''  We  wander  through  a  dense  park,  into  which  vistas  of 
rare  beauty  open  up  at  almost  every  point.  Here  the  dis- 
tant valley  unfolds  itself  a  boundless  panorama;  there 
the  majestic  cone  of  Orizaba,  white  with  the  frost  of  ages, 
towers  far  into  the  region  of  eternal  cloudland." 

At  an  elevation  of  between  10,000  and  10,500  feet,  a 
belt  of  spruce  trees  [Abies  religiosa)  was  entered,  but,  on 
its  lower  margin,  oaks  had  already  begun  to  appear.  The 
pine,  however,  still  continues  to  be  the  dominant  form  of 
arborescent  vegetation.  Flowering  plants  were  not  spe- 
cially numerous,  the  most  noticeable  being  a  lupine  and 
several  species  of  senecio.  At  an  elevation  of  about 
12,000  feet,  the  forests  terminate,  and  a  broad,  open, 
grass-covered  belt  encircles  the  cone  below  the  lower  limit 
of  perennial  snow. 

The  divide  between  the  Sierra  Negra  and  the  peak  of 


VOLCANOES    OF    MEXICO 


177 


Orizaba  offers  a  splendid  view  of  each  of  these  volcanoes. 
The  former  barely  reaches  the  line  of  perpetual  snow, 
and  shows  well  the  effects  of  long-continued  atmospheric 
erosion ;  the  latter,  white  with  frost,  retains  the  con- 
tours which  were  impressed  upon  it  at  about  the  time  of 
the  last  eruption.  At  various  places  on  the  flanks  of 
Orizaba  dark  buttresses  of  rock  stand  out  in  vertical 
masses,  showing  where  eruptions  of  greater  or  less  mag- 
nitude have  marked  epochs  in  the  history  of  the  mountain. 
Huge  outwellings  of  lava  seam  the  slopes  in  radiating 
lines,  but  they  belong  in  great  part  to  a  period  of  volcanic 
activity  when  the  centre  of  eruption  was  located  some 
little  distance  from  the  site  of  the  present  crater. 

At  an  elevation  of  14,500  to  15,000  feet,  the  zone  of 
grasses  terminates  with  an  irregular  edge.  With  the 
grasses  are  a  few  flowering  plants. 

The  last  traces  of  terrestrial  animal  life  occur  at  about 
15,000  feet,  where,  Heilprin  says,  "  we  picked  up  a  soli- 
tary lizard  from  one  of  the  sun-warmed  boulders.  There 
were  no  msects,  at  least  we  failed  to  find  any  traces  of 
their  existence,  at  this  altitude.  But  birds  were  still 
observed  and  heard  above  us ;  we  thought  we  recognized 
the  tit  and  the  chickadee,  and  possibly  a  species  of  wren. 
There  was  no  question  as  to  the  raven,  whose  '  caw '  was 
heard  far  o'ertop  of  us,  or  the  sparrow-hawk.  At  about 
one  o'clock  we  reached  the  ice-cap  [elevation  15,500  feet], 
which  is  here  split  by  a  ridge  of  rock  and  boulders  enter- 
ing far  into  its  limits.  .  .  .  The  snow  field,  or  more  cor- 
rectly ice  field,  was  of  inconsiderable  development,  at  no 
point  when  seen  by  us  attaining  a  greater  thickness  than 
about  5-7  feet.  Its  surface  was  everywhere  cut  up  into 
sharp  pinnacles  (seracs)  two  or  three  feet  in  height,  which, 


I 


4  i 


178 


VOLCANOES   OP   NORTH    AMERICA 


(; 


I  i 


i 


wliilo  (^fT((ring  safe  lod^ornont  to  tlio  feot,  rendorod  progress 
exceedingly  irksoine.  There  was  no  soft  snow,  and  the 
feet  made  Init  little  impression  on  the  crusty  surface  of 
the  ice." 

In  ascending  Orizaba  when  the  sky  is  clear,  magnifi- 
cent views  are  obtained  of  the  great  tableland  of  central 
Mexico  on  the  west,  and  of  the  shore  of  the  Gulf  on  the 
east.  As  described  by  Heilprin,  at  an  elevation  of  15,000 
feet,  the  lofty  sunnnits  of  Popocatepetl  and  Ixtaccihuatl 
came  into  view,  through  the  haze,  although  one  hundred 
miles  or  more  distant,  and  were  boldly  outlined  against 
the  western  sky.  As  in  most  high  mountains,  however, 
the  truly  picturesque  scenes  are  to  be  observed  from  the 
lower  slopes.  Views  from  lofty  summits  resemble  maps 
rather  than  pictures. 

In  comparison  with  many  other  mountains  of  similar 
height,  Orizaba  is  easy  of  ascent.  The  height  of  the  tim- 
ber line,  12,000  feet,  leaves  but  GOOO  feet  above  the  high- 
est camp  fire.  The  elevation  above  the  point  at  which 
a  camp  can  be  established,  furnishes  a  rough  measure, 
in  many  instances,  of  the  difficulties  to  be  overcome  in 
mountain  climbing.  Heilprin  states  that  from  bottom 
to  top,  there  are  no  precipices  to  climb,  no  impending 
ledges  to  crawl  around  or  over,  and  no  glaciers  to  cross. 
In  these  respects  Orizaba  agrees  with  Popocatepetl,  while 
it  differs  greatly  from  Ixtaccihuatl.  "The  slope  from  the 
plateau  base  to  the  summit  is  pleasingly  gentle  and  uni- 
form, and  the  traveller  who  is  bent  upon  making  the 
attack  requires  merely  a  staff,  proper  foot  gear,  and  a 
good  constitution." 

Popocatepetl.  —  The  second  mountain  in  Mexico  in 
reference   to   altitude   is   Popocatepetl,  or  the   Smoking 


■^ 


VOLCANOES   OF    MHXICO 


IT'.t 


Mountain.  Triangulations  made  by  Ilinnltolclt '  in  1S04 
gave  17,728  feet,  wliile  aneroid  ineasurenienLs  by  Ileil- 
prin-  in  1889,  already  referred  to,  gave  17,0-;}  feut  as 
the  lieigbt  of  the  summit.  M(jre  reeent  measurements 
by  tlie  Mexican  Geological  Survey'  place  the  elevation 
at  17,870  feet. 

For  many  years  Popocatepetl  was  thought  to  he  the 
highest  mountain  in  North  America,  hut  it  is  now 
known  to  be  surpassed  by  at  least  three  other  peaks 
on  this  continent. 

Popocatepetl  is  a  conical  peak  with  a  depression  i)Y 
crater  in  its  sunnnit.  On  the  rim  of  the  crater  there 
are  two  prominent  crags,  connected  Ijy  a  narrow  ridge  ; 
the  higher  of  these  is  known  as  Pico  Mavor.  and  the  other 
has  been  named  Espinazo  del  Diablo.  The  bottom  of  the 
crater  is  1056  feet  below  the  summit  of  the  highest  spire 
on  its  rim;  the  surface  diameter  of  the  great  bowl  is 
about  2000  feet.  From  fissures  in  the  bottom  of  the 
crater  steam  still  escapes,  but  the  heat  is  not  sullicient 
to  melt  the  winter's  snow,  which  reaches  a  depth  oi  eight 
or  ten  feet,  and  covers  the  outer  slopes  of  the  mountain 
down  to  an  elevation  on  the  north  side,  of  14, '^08  feet. 
A  thousand  feet  below  the  snow  line  is  the  upper  limit 
of  vegetation.  All  of  the  lower  slopes  are  clothed  with 
forests,  which  in  places  attain  a  tropical  luxuriance.  The 
melting  snows  supply  a  small  lake  in  the  crater,  and  the 
water  percolating  through  the  porous  lava-sand  feeds 
copious  thermal  springs  about  the  base  of  the  mountain. 


1"  Cosmos,"  New  York,  1869,  Vol.  V,  p.  127. 
2 Philadelphia  Acad.  Nat.  Sci.,  Proc,  1890,  pp.  251-20;j. 
'J.  G.  Aguilera  and  E.Ordonez,  "Expedicion  cienti'tica  al  Popocatepetl," 
Mexico,  1895. 


/ 


180 


VOLCANOES   OF   NOUTH    AMEUICA 


t.l 


! 


I'll 


t 


i!^ 


A. 


Tliis  percolation  of  moteoric  water  tli rough  the  rocks, 
illustrates  one  t)f  the  important  [)rocess(»s  by  which  a 
volcanic  mountain  parts  with  its  heat. 

ro[>ocatepetl  stands  on  the  eastern  edge  of  the  great 
central  plateau  of  Mexico.  On  one  side  it  looks  down 
on  the  capital  of  the  Republic,  and  on  the  other  descends 
into  the  tropical  lowlands  bordering  the  central  plateau. 
The  visual  height,  as  seen  from  the  city  of  Mexico,  is 
10,00(1  feet ;  and  from  the  lowland  to  the  eastward,  about 
17,000  feet.  Seen  from  the  basal  plains,  it  sweeps  up  in 
one  grand  curve  to  nearly  its  full  height,  —  a  colossus  of 
three  and  a  quarter  miles  in  elevation,  white  with  ever- 
lasting frost  on  its  summit,  and  bathed  in  the  green  of 
palms,  bananas,  oranges,  and  mangoes  at  its  Imse.  Ever- 
green oaks  and  pines  encircle  its  middle  height,  and  above 
them,  l)efore  the  ice  itself  is  reached,  occur  broad  areas 
of  loose  sand  into  which  the  lavas  have  been  changed  by 
weathering.  Soft  wreaths  of  sulphurous  vapor  may  at 
times  be  seen  curling  over  the  crest  of  the  summit  crater, 
—  gentle  reminders  that  the  days  of  volcanic  activity  are 
not  yet  necessarily  over. 

The  ascent  of  Popocatepetl,  as  stat-^d  l)y  Ileilprin,^  is 
neither  a  difficult  or  dangerous  task.  One  or  more  as- 
cents are  probably  made  each  year.  Horses  can  mount 
without  much  difficulty  to  an  elevation  of  13,000  or 
14,000  feet,  and  might  be  urged  still  higher.  The  view 
from  the  summit  is  almost  incomparably  grand,  reaching 
on  clear  days  from  the  Gulf  of  Mexico  almost  to  the 
Pacific.  In  three  directions  the  view  is  unbroken  except 
by  the  limitations  of  vision ;  on  the  fourth  (to  the  north) 

*  "Around  the  World"  (a  magazine  published  in  Philadelphia),  Vol.  1, 
1894,  p.  13,  with  a  fine  illustration. 


1  ;     i 


^p 


VOLC/VNOES   OF    MKXKMJ 


181 


it  om])raroa  a  colossus  of  nearly  tlio  saino  Ijoi^lit  as  the 
great  "  vSmokinj;;  Mountain"  itself,  the  famous  Ixtaccihu- 
atl,  or  "  White  Woman." 

AlihoUjL^h  rising  fully  oOOO  feet  above  the  snow  line, 
its  snowy  covering  is  inecMisiderable  ;  ranjly  (lo(>s  it  meas- 
ure more  than  three  to  six  feet  in  depth.  Nothing  worthy 
to  be  considered  as  a  glacier  is  found  on  the  mountain. 

Many  a.scents  of  Popocatepetl  have  been  made  not  only 
by  travellers,  but  by  volcaneros,  who  gather  sulphur  from 
the  crater.  It  has  been  estimated  that  about  fifty  tons 
of  sulphur  are  obtained  annually,  the  supi)ly  being  re- 
newed by  condensation  from  escaping  vapors.  The  crude 
methods  heretofore  employed  to  gather  and  transport  tliL* 
sulphur,  arc  to  be  sup[)lanted,  it  is  said,  Ijy  mure  en- 
lightened processes,  under  the  management  of  a  syndicate. 

In  1895,  a  short  account  was  published  of  a  scientific 
expedition  to  Popocatepetl,  by  the  Mexican  Geological 
Survey,'  which  adds  nuich  to  the  geological  history  of  the 
mountain  previously  recorded. 

The  crater  is  described  by  the  explorers  just  mentioned, 
who  spent  twenty-eight  hours  in  examining  it,  as  ellip- 
tical in  outline,  with  sloping  walls,  and  with  axes  measur- 
ing G12  and  400  metres,  respectively.  Owing  to  marked 
irregularities  in  the  height  of  the  rim  of  the  crater,  its 
depth  may  be  variously  stated.  Its  bottom  is  505  metres 
below  the  summit  of  the  highest  pinnacle,  Pico  Mayor, 
and  205  metres  below  the  lowest  point  on  its  rim. 

"Popocatepetl  is  a  cone  formed  by  an  accumulation  of 
many  successive  currents  of  lava,  covered  with  fragmen- 

*  J.  G.  Aguilera  and  Ezequiel  Ordonez,  "  Expedicion  cientifica  al  Popo- 
catepetl," pp.  1-48,  PL  1-G.  The  notes  here  quoted  are  from  an  abstract  of 
the  report  printed  in  the  "American  Geologist,"  Vol.  XVII,  1890,  pp.  330, 
331. 


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182 


VOLCANOES   OF  NORTH   AMERICA 


tary  materials,  stones,  sand,  ashes,  etc.,  and  corresponds 
to  those  volcanoes  called  by  some  geologists  '  stratified 
cones.'  The  lower  or  older  of  these  currents  shows  a 
rock  structure  more  granular  and  less  lustrous  than  that 
of  the  later  ones.  Polarized  light  also  reveals  a  crystal- 
line development  in  the  former,  which  is  not  found  in  the 
more  glassy  and  amorphous  structure  of  the  latter.  From 
these  and  other  facts,  the  authors  deduce  the  conclusion 
that  the  history  of  the  volcano  has  been  marked  by  three 
stages,  which  they  denominate  penodo  cinerorjeno,  ^;c;70f/o 
brechofjoio,  and  ijerlodo  Idvico.  The  earliest,  the  lava 
period,  was  the  lon,G:est ;  during  the  second,  the  ejecta 
consisted  largely  of  pumice,  mixed  at  times  with  volcanic 
bombs  —  blocks  of  andesite  of  the  same  nature  as  the  lava; 
the  third  has  supplied  showers  of  ashes,  which  overlie  the 
older  products  and  have  been  much  eroded  by  winds  and 
rain.  These  periods  the  authors  correlate  with  the  Plio- 
cene, Pleistocene,  and  Recent.  Some  of  the  earlier  ande- 
site lava  flows  are  buried  beneath  beds  containinuj  remains 
of  the  horse  and  elephant,  while  a  stream  of  very  liquid 
basalt  from  the  neighboring  peak  of  Xitli  overlies  not 
only  deposits  containing  vertebrate  fossils,  but  even  hu- 
man remains. 

"Three  kinds  of  eruptive  matter  are  defined,  —  labra- 
dorite-basalt,  hypersthene-andesite,  and  trachyte,  of  which 
the  first  is  the  oldest,  and  is  found  in  the  lowest  currents ; 
but  the  grand  cone  is  mostly  composed  of  the  second, 
which  varies  in  structure  from  holocrystalline  to  vitreous, 
while  the  little  summits  consist  of  the  third  kind  of 
ejecta. 

"In  the  various  facts  given,  the  authors  see  a  record  of 
the  original  great  energy  and  gradual  decay  of  the  vol- 


VOLCANOES   OF   MEXICO 


183 


canic  action  which  has  now  ahnost  ceased,  nothing  but 
smoke  and  vapor  issuing  from  the  cone." 

As  stated  by  Rechis,'  there  are  reasons  for  believino" 
that  the  first  person  who  ascended  Popocatepetl  was  the 
Spanish  captain,  Diego  de  Ordaz,  who  was  with  Cortes  in 
1519,  but  authorities  are  cited  which  render  it  uncertain 
tliat  he  gained  the  summit. 

Ixtaccihuatl.  —  Rising  to  the  north  of  Popocatepetl,  and, 
like  its  greater  neighbor,  in  full  view  from  the  city  of 
Mexico,  stands  Ixtaccihuatl,  or  the  "White  Woman," 
as  the  mountain  was  named  by  the  Aztecs.  The  sum- 
mits of  these  two  giant  peaks  are  barely  len  miles  apart. 
The  description  of  an  ascent  of  Popocatepetl,  already 
cited,  would  apply  in  all  its  general  features  to  its  near 
neighbor,  and  need  not  be  repeated. 

The  height  of  Ixtaccihuatl  is  given  by  Heilprin  as 
16,960  feet,  but  other  measurements,  whicli  so  far  as 
can  be  judged  are  equally  trustworthy,  make  it  some  500 
feet  less.  Some  writers  have  asserted  that  this  grand 
peak  is  not  of  volcanic  origin,  but  fail  to  give  reasons 
for  considering  it  to  have  a  different  history  than  the 
neighboring  volcanoes,  which  it  closely  resembles.  Its 
conical  form  and  the  fact  that  it  is  largely  composed 
of  trachytic  rocks,  seem  to  show  that  it  owes  its  promi- 
nence to  volcanic  agencies.  It  is  evidently  older  than 
Popocatepetl,  and  has  undoubtedly  been  decreased  in 
height  by  erosion.  There  is  no  crater  at  the  summit, 
and  no  evidence  of  lingering  volcanic  heat.  The  sum- 
mit is  snow-capped  even  in  summer.  The  original  crater 
may  reasonably  be  supposed  to  have  been  filled  by  the 

^  jfilisee  Reclus,  "The  Earth  and  its  Inhabitants:  Morth  America,"  New 
York,  1891,  Vol.  II,  p.  27. 


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VOLCANOES   OF   NORTH   AMERICA 


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washing  in  of  its  sides,  and  the  summit  angle  of  the 
peak  bhmted  by  the  same  process. 

Xinantecatl.  —  Al^out  forty  miles  southwest  of  the 
city  of  Mexico  near  the  city  of  Toluca,  rises  a  symmetri- 
cal volcanic  pile  with  gentle  slopes,  to  a  height  of  about 
15,000  xcet,  which  is  known  as  Nevado  de  Toluca,  or  the 
"Snow  of  Toluca."  Its  Aztec  name  is  Xinantecatl, or  the 
"  Naked  Lord." 

The  summit  of  Xinantecatl,  as  seen  from  the  south, 
barely  reaches  the  lower  limit  of  perpetual  snow,  but  its 
northern  side  is  v/hite,  even  in  September  and  October, 
the  months  when  the  melting  and  evaporation  of  the 
snow  is  most  advanced.  In  the  summit  of  the  peak  there 
are  two  craters,  which  are  now  flooded  and  form  lakes  of 
fresh  water,  with  a  combined  area  of  about  eighty  acres. 
The  larger  lake  is  reputed  to  be  thirty  feet  deep  and 
inhabited  by  fish  of  a  peculiar  species. 

Xinantecatl  furnishes  an  example  of  an  extinct  or 
dormant  volcano,  and  serves  to  connect  in  one  series 
certain  older  volcanoes  like  Ixtaccihuatl,  which  have  been 
exposed  to  storms  and  frosts  for  such  a  length  of  time 
that  their  craters  have  disappeared,  with  volcanic  moun- 
tains of  recent  date  like  Popocatepetl,  which  not  only 
still  retain  their  summit  craters  but  are  yet  giving  out 
steam  and  heated  gases. 

Tuxtla. — Volcan  de  Tuxtla,  situated  on  the  coast  of 
the  Gulf  of  Mexico,  about  eighty  miles  southeast  of  Vera 
Cruz,  is  reported  to  be  ^.950  feet  high.  In  1664,  it 
erupted  molten  lava,  but  again  became  quiescent,  until 
March,  1793,  when  one  of  the  grandest  volcanic  outbreaks 
of  modern  times  occurred.  This  eruption  was  of  the 
explosive  type,  and  rivalled  in  energy  the  catastrophe  that 


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VOLCANOES   OF   MEXICO 


185 


blew  away  the  summit  of  Conseguina  in  1835.  Scoria, 
lapilli,  and  dust  were  blown  into  the  air  with  such 
violence  that  they  rosn  thousands  of  feet  and  were 
carried  by  the  wind  150  miles  towards  the  northwest, 
and  about  the  same  distance  to  the  southwest.  The 
roofs  of  houses  in  Vera  Cruz,  Perote,  and  Oaxaca  were 
covered  with  lapilli  and  dust.  The  noise  of  the  explo- 
sion sounded  like  heavy  guns  and  was  heard  distinctly 
at  Perote,  about  150  miles  to  the  northwest. 

Suice  the  great  eruption  just  referred  to,  less  violent 
discharges  from  the  same  vent  have  taken  place.  The 
small  height  of  Tuxtla  is  due  to  the  blowing  away  of  the 
summit  of  the  mountain  during  a  great  explosion  in 
1793,  and  illustrates  the  fact  that  young  and  energetic 
volcanic  mountains  are  not  necessarily  lofty.  Mild  explo- 
sions, if  long  continued,  tend  to  build  up  symmetrical 
peaks  with  gracefully  curving  slopes,  but  when  the  energy 
of  the  explosions  increases,  the  summits  of  the  volcanoes 
in  which  they  occur  are  frequently  blown  away,  and  the 
fragments  distributed  far  and  wide  over  the  adjacent 
region.  Low  mountains  with  abnormally  large  craters 
are  the  results  of  such  catastrophes.  In  fact,  when  the 
explosions  are  excessively  violent,  nothing  to  suggest  a 
mountain  remains,  but  great  pits  in  the  earth  without 
elevated  rims  sometimes  result.  This  is  forcibly  illus- 
trated in  the  case  of  Krakatoa  in  1883,  already  described, 
when  not  only  was  a  mountain  blown  away,  but  a  depres- 
sion 3000  feet  deep  left  to  mark  its  site.  It  does  not 
follow,  however,  that  all  large  craters,  "calderas,"  and 
"  crater-rings,"  are  to  be  accounted  for  in  this  manner,  as 
the  drawing  off  of  the  liquid  lava  from  a  crater  and  the 
tumbling  in  of  its  walls  may  produce  similar  results. 


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VOLCANOES  OF   NOUTH   AMEIIICA 


Cofre  de  Perote.  —  About  thirty  miles  north  of  the 
peak  of  Orizaba,  there  stands  a  mountain  about  13,552 
feet  high,  with  a  quadranguhir  summit.  When  seen  from 
the  neigliboring  portion  of  the  Gulf  of  Mexico,  the  sum- 
mit of  the  peak  has  a  resemblance  to  a  coffer,  or  sar- 
cophagus, which  has  suggested  its  modern  name.  To 
the  Aztecs  it  was  known  as  Nauhcampa-tepetl,  or  "  Four- 
ridged  Mountain."  Surrounding  the  base  of  the  moun- 
tain, and  evidently  originating  from  it,  is  a  deposit  of  lava 
and  pumice,  which  gives  the  country  an  uneven  surface, 
and  has  gained  for  it  the  name  malajxiis  or  "bad  country." 
This  term  is  used  in  several  parts  of  Mexico  for  rugged 
lava  flows  and  has  been  adopted  somewhat  generally  by 
American  geologists  as  a  technical  name  for  lava  sheets 
with  rough  surfaces  composed  of  angular  blocks  of  rock, 
similar  to  the  aa  surfaces  of  the  lava  streams  of  Hawaii. 
The  Cofre  was  ascended  by  Humboldt  in  1804  and  its  alti- 
tude and  position  determined.  Nothing  of  the  nature  of 
a  crater  was  found  at  the  summit,  but  the  rock  of  which 
the  mountain  is  largely  composed  is  termed  a  dlorlt'ic 
trachyte.  Streams  of  hardened  lava  radiate  from  the 
mountain,  and  record  the  energy  of  its  ancient  discharges. 
Humboldt  found  only  isolated  patches  of  snow  about  the 
summit  in  the  month  of  February,  which  reached  down 
to  a  limit  of  12,500  feet,  and  about  700  or  800  feet  below 
the  upper  limit  of  forest  growth.  The  top  is  bare  of 
snow  in  late  summer  and  autumn. 

The  Cofre  is  evidently  a  volcanic  cone  that  has  passed 
its  youth  and  has  yielded,  to  a  marked  degi-ee,  to  the 
attacks  of  erosive  agencies.  To  Humboldt  it  appeared 
to  furnish  an  example  of  a  mountain  upraised  by  forces 
acting  from  beneath  and  to  be  a  "crater  of  elevation." 


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VOLCANOES   OB"   MEXICO 


187 


This  hypothesis  to  account  for   the   origin   of   volcanic 
mountains  has  for  the  most  part  been  abandoned,  for  the 
reason  that  it  is  now  well  known  that  volcanoes  build  up 
elevations  by  extruding  lava  and  by  blowing  out  projec- 
tiles which    accunudate  about  the   opening   from   which 
they  came,  but  not  by  pronounced  upheaval  of  the  earth's 
crust.     Humboldt's  account  of  the  Cofre  is  of  interest  as 
illustrating  his  hypothesis  of  the  origin  of  volcanic  moun- 
tains by  upheaval,  as  well  as  for  the  observed  facts  it  con- 
tains.    He  says  ^ :  "  In  ascending  the  mountain  I  saw  no 
trace  of  the  falling  in  of  a  crater,  or  of  eruptive  orifices 
on  its  declivities ;  no  masses  of  scoria),  and  no  obsidians, 
pearlites,  or  pumice-stones  belonging  to  it.     The  blackish- 
gray  rock  is  very  uniformly  composed  of  much  hornblende 
and  a  species  of  feldspar,  which  is  not  glassy  feldspar 
(sanidine)   but   oligoclase ;    this   would    show   the   entire 
rock,  which  is  not  porous,  to  be  a  dioritic  trachyte.     I 
describe  the    impressions  wdiich    I    experienced.     If    the 
terrible,    black    lava    fields  —  malapais  —  (upon    which   I 
have    here   purposely  dwelt   in  order  to  counteract   the 
too  one-sided  consideration  of  exertions  of  volcanic  force 
from  the  interior)  did  not  flow  from  the  Cofre  de  Perote 
itself  at  a  lateral  opening,  still  the  upheaval  of  this  iso- 
lated mountain,  13,553  feet  in  height,  may  have  caused 
the  formation  of   the  Loma  de  Tobias    [the   flat-topped 
summit  rock  from  which  the  mountain  derives  its  name]. 
During  such  an  upheaval,  longitudinal  fissures  and  net- 
works of  fissures  may  be  produced  far  and  wide  by  fold- 
ing of  the  soil,  and  from  these  molten  masses  may  have 
poured  directly,  sometimes  as  dense  masses,  and  some- 
times as  scoriaceous  lava,  without  any  formation  of  true 

»«  Cosmos,"  New  York,  1869,  Vol.  V,  pp.  308,  309. 


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VOLCANOES  OF  NORTH  AMERICA 


mountain  platforms  (open  cones  or  craters  of  elevation). 
Do  we  not  seek  in  vain  in  the  great  mountains  of  basalt 
and  porpliyritic  slate  for  central  points  (crater  moun- 
tains), or  lower  circumvallated,  circular  chasms,  to  which 
their  common  production  might  be  ascribed  ?  " 

This  is  only  a  portion  of  Humboldt's  discussion  of  the 
origin  of  volcanic  mountains,  presented  in  connection 
with  his  account  of  the  Cofre,  but  nowhere  does  he  seem 
to  recognize  the  clianges  that  a  mountain  passes  through 
when  subjected  to  the  destructive  influence  of  the  atmos- 
phere. If  one  has  in  mind  the  fact  that  a  mountain 
with  an  open  crater  at  the  summit  may,  by  erosion,  be 
transformed  into  a  more  obtuse  cone,  or  bell-shaped  pile, 
by  having  the  crater  walls  removed,  many  of  the  difficul- 
ties encountered  by  geologists  half  a  century  or  more  ago 
disappear;  and  a  sequence  of  topographic  forms  due  to 
volcanic  extrusion,  and  another  equally  interesting  series 
resulting  from  decay,  disintegration,  and  erosion,  come 
into  view. 

Colima.  —  On  the  west  coa^t  of  Mexico,  and  bearing 
much  the  same  relation  to  the  seaport  of  Manzanillo 
that  Tuxtla  does  to  Vera  Cruz,  is  a  volcano  known  as 
Colima.  As  stated  by  Humboldt,  Colima  is  about  5500 
feet  high,  and  at  the  time  of  his  visit  to  Mexico,  fre- 
quently ejected  lapilli,  accompanied  by  vapor.  It  pre- 
sents a  fine  sight  from  the  town  of  Colima,  from  which 
it  takes  its  name.  In  winter  it  is  frequently  whHened 
w  :th   snow. 

In  recent  years,  Colima  has  been  more  active  than  dur- 
ing the  earlier  portion  of  the  present  century.  Eruptions 
occurred  in  1869,  1872,  and  1873.  In  1885  lapilli  was 
thrown  out  and  carried  by  the  wind  280  miles  to  the 


^  / 


VOLCANOES   OF  MEXICO 


189 


northeast.  Lava  was  also  discharged  during  these  erup- 
tions, but  nearly  always  from  lateral  openings,  the  "  sons 
of  Colima  "  as  they  are  locally  termed,  and  formed  small 
craters  on  the  adjacent  plain.' 

Ceboruco,  or  Ahuacatlan. — This  mountain,  with  an 
elevation  of  about  7140  feet,  rises  near  the  Pacific  coast, 
a  few  miles  south  of  San  Bias,  and  is  the  most  northerly 
of  the  recently  active  volcanoes  of  Mexico.  In  1870,  it 
became  violently  active,  and  since  then  has  never  ceased 
to  emit  steam.  The  volcano  is  the  centre  of  a  group  of 
craters.  Of  these  there  are  two  of  large  size  and  about 
1000  feet  deep  each,  one  of  which  still  emits  steam, 
but  the  other  is  to  all  appearance  extinct.' 

Volcanoes  of  Northern  Mexico.  —  To  enumerate  the 
remainder  of  the  active  or  recently  extinct  volcanoes  of 
Mexico,  concerning  which  general  information  is  avail- 
able, would  necessitate  much  repetition,  and  probably 
lead  to  confusion  instead  of  serving  to  illustrate  the 
laws  which  govern  volcanic  action. 

North  of  the  region  in  south-central  Mexico,  which  is 
studded  with  great  volcanic  mountains  and  is  a  direct 
continuation,  but  marked  by  a  conspicuous  increase  in 
breadth,  of  the  Central  American  volcanic  chain,  there 
are  broad  fields  of  rugged  lava  with  a  considerable  num- 
ber of  craters  in  various  stages  of  decay  and  dilapidation. 
This  broader  portion  of  the  volcanic  belt  already  referred 
to,  without  active  craters,  belongs  geographically  with 
the  still  broader  region  of  former  volcanic  activity  in 
the  United  States  and  extending  for  an  undetermined  dis- 
tance into  Canada,  and  does  not  claim  special  attention  at 
this  time. 

1  Reclus,  "North  America,"  Vol.  II,  1891,  p.  24. 


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VOLCANOES   OF   NORTH   AMERICA 


Volcanoes  of  Lower  California.  —  In  the  portion  of 
Mexico  known  as  Lower  Ciilifornica,  volcanic  mountains 
and  lava  fields  also  occur ;  but  in  the  absence  of  scientific 
exploration  little  need  be  said  concerning  them.  From 
various  sources  I  learn  that  Lower  California  is  traversed 
from  north  to  south  by  an  elevated  region,  much  of  which 
is  composed  of  volcanic  rocks.  The  highest  summits  are 
at  the  north,  where  Mt.  Calamahue,  or  Santa  Catalina, 
rises  to  a  height  of  approximately  10,000  feet  and  reaches 
the  lower  limit  of  perpetual  snow. 

Midway  down  the  Peninsula,  and  overlooking  the  Gulf 
on  the  east,  stands  a  group  of  volcanic  peaks  known  as 
the  Tres  Virgenes,  which  are  reported  to  be  from  G600 
to  7250  feet  high.  An  eruption  occurred  in  this  group 
in  1857,  and  since  then  steam  has  been  emitted,  some- 
times in  large  volumes. 


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CHAPTER   V 

VOLCANOES  OF  THE   UNITED  STATES 

(Tho  distribution  of  the  principal  volcanoes  of  the  United  Statis  is  sliown  in 

riate  4.) 

A  GENERAL  account  of  the  distribution  of  the  volcanoes 
of  the  United  States  has  already  been  given.  It  will  be 
remembered  that  they  occur  in  the  Cordilleran  region  to 
the  west  of  the  meridian  of  Denver. 

In  the  Cordilleran  region  the  surface  rocks  iirc  largely 
of  igneous  origin.  Nearly  every  mountain  range  has  an 
igneous  core  or  has  lava  sheets  or  craters  associated 
with  it.  In  several  instances  entire  mountain  rantres 
are  composed  of  rocks  that  were  once  molten.  The 
rocks  referred  to  are  of  all  ages,  from  the  Archaean  to 
recent  times.  It  is  only  to  those  of  volcanic  origin,  how- 
ever, and  of  such  a  late  date  that  but  moderate  changes 
have  resulted  from  erosive  agencies,  that  attention  is  here 
invited.  The  lava  flows  in  numerous  instances  are  still 
rough  and  bare  of  vegetation,  and  the  craters  as  perfect 
in  outline  as  when  still  steaming. 

It  does  not  seem  desirable  at  this  time  to  attempt  a 
minute  description  of  the  hundreds  of  lava  flows  and 
craters  within  the  United  States,  even  if  the  investiga- 
tion of  this  branch  of  the  ancient  history  of  our  country 
was  sufficiently  advanced  to  make  such  a  course  possible. 

191 


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VOLCANOES   OP   NORTH   AMEUICA 


My  plan,  thorcforo,  will  bo  to  select  a  few  typical  ex- 
amples of  volcanic  mountains  and  of  lava  sheets,  for 
presentation. 

San  Francisco  Mountain,  Arizona,  and  Adjacent  Craters. 
—  The  highest  and  most  prominent  group  of  mountain 
peaks  in  the  southwestern  portion  of  the  United  States 
is  in  northern  Arizona,  about  twelve  miles  north  of  the 
town  of  Flagstaff,  and  known  as  the  San  Francisco  moun- 
tains.  (Plate  G,  Fig.  A.)  The  Atlantic  and  Pacific  rail- 
road passes  through  Flagstaff,  and  passengers  by  that 
route  usually  have  many  fine  views  of  the  neighboring 
mountains,  through  the  open  forest  of  puies  that  clothes 
the  plateau  on  which  they  stand,  and  extends  far  up  their 
sides.  The  highest  peak  rises  12,562  feet  above  the  sea, 
and  5700  feet  above  the  general  level  of  the  surrounding 
tableland. 

The  San  Francisco  group,  according  to  G.  K.  Gilbert,^ 
includes  a  series  of  large  peaks  of  trachyte,  the  products 
of  massive  eruptions,  and  a  multitude  of  small  scoria 
cones,  associated  with  broad  and,  in  part,  thick  sheets 
of  basaltic  lava. 

The  larger  cones  are  of  comparatively  ancient  date, 
possibly  Tertiary,  and  are  much  wasted  by  erosion.  The 
summits  are  sharp,  their  sides  deeply  scored  with  ravines, 
and  nothing  to  represent  a  crater  remains. 

Much  more  recent  than  the  main  peaks  are  the  smaller 
craters  of  black  basalt  adjoining  them,  especially  to  the 
eastward.  Many  of  these  craters  are  as  perfect  as  when 
first  formed.  The  streams  of  black,  scoriaceous  lava  that 
escaped  from  some  of  them  and  spread  out  on  the  sur- 

^  "  Geographical  and  Geological  Explorations  and  Surveys  West  of  the 
100th  Meridian,"  Vol.  Ill,  <'  Geology,"  1875,  pp.  129,  130. 


\ 


VOLCANOEa   OF  TIIK   UNITED   STATES 


lOfl 


ts 


rounding  plain,  are  so  frosli  in  appoaranco  tiiat  to  an 
observer  looking  down  on  them  ironi  the  sides  of  the 
main  elevations,  they  seem  scarcely  to  have  cooled  from 
their  original  molten  condition.  The  number  of  these 
recent  vents  is  stated  by  Gilbert  to  be  some  hundreds. 
As  many  as  one  hundred  are  marked  by  cinder  cones. 
Sixty-five  with  craters  partially  or  wholly  preserved 
m.iy  be  counted.  Some  of  the  craters  are  intensely 
black,  with  large  areas  of  dark  red  where  oxidation 
has  taken  place,  and  are  entirely  free  of  vegetation ;  on 
others,  de.sert  shrubs  have  ascended  the  slopes,  and  con- 
ceal in  part  the  ruggedness  of  the  angular  and  broken 
lava  and  scoria.  At  least  one  of  the  craters  contains  a 
lake.  A  view  over  this  desert  of  lava  studded  with 
craters  several  hundred  feet  high,  some  of  which  have 
great  gaps  in  their  rims  through  which  floods  of  molten 
lava  once  escaped,  calls  vividly  to  mind  the  illustrations 
published  by  Scrope,'  of  the  now  classic  volcanoes  of 
central  France. 

Mt.  Taylor,'^  New  Mexico.  —  The  western  part  of 
New  Mexico  owes  much  of  its  characteristic  scenery  to 
the  presence  of  high  tablelands,  separated  by  regions  of 
deep  erosion.  One  of  these  tablelands,  or  mesas,  is  cov- 
ered with  lava  flows,  and  sustains  a  prominent  volcanic 
pile  named  Mt.  Taylor.  The  mountain  has  an  eleva- 
tion of  11,390  feet  above  the  sea.  The  mesa  from  which 
it  rises  is  forty-seven  miles  long  from  northeast  to  south- 


*  G.  P.  Scrope,  "  The  Geology  and  Extinct  Volcanoes  of  Central  France," 
London,  1858,  PL  3,  5. 

"  The  most  readily  available  source  of  information  concerning  Mt. 
Taylor  and  the  adjacent  region,  is  "  Mt.  Taylor  and  the  Zuni  Plateau," 
by  C.  E.  Button,  in  the  6th  Annual  Report  of  the  U.  S.  Geological  Sur- 
vey, 1884-85,  pp.  105-198. 


3 


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VOLCANflES   OF    NORTH    AMKUICA 


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west,  and  twonty-tliroo  miles  Ijpoad.  Its  TiiMrL^iii.s  are  ir- 
rc^^nilar  and  deeply  indented.  It  lias  a  general  elevat'on 
ol"  8200  feet,  and  rises  in  general  2000  feet  altove  tlu?  more 
thorongldy  eroded  (tonntry  with  which  it  is  snrronndcMl. 
The  mesa  is  a  n^lic  left  hy  erosion,  and  fnrnislies  a  meas- 
nre  of  a  portion  of  the  general  lowering  of  the  snrface  of 
the  adjacent  conntry.  that  has  taken  plac(»  owing  to  the 
action  of  rain,  rivcsrs,  and  other  dennding  agencies.  The 
reason  why  the  rocks  forming  the  hasement  layer  of  the 
mesa  have  escaped  destruction  and  caused  it  to  hecome  a 
prominent  topographical  feature  as  the  adjacent  region 
was  lowered,  is  because  of  a  surface  layer  of  lava  about 
300  feet  thick,  which  resisted  the  attack  of  atmo.spheric 
agencies  nuicli  more  effectually  than  the  sedimentary 
strata  surrounding  it.  The  Mt.  Taylor  mesa  and  neigh- 
boring elevated  areas  of  the  same  general  nature,  are 
literally  roofed  with  lava,  which  has  shed  off  the  rain, 
and  protected  the  strata  beneath. 

Mt.  Taylor  is  composed  almost  entirely  of  lava, 
which  rose  through  a  single  opening  and  built  up  a  promi- 
nent cone  with  a  large  crater  in  the  summit.  The  primi- 
tive form  is  now  greatly  altered  by  erosion.  It  stands 
as  a  ruin,  in  which  one  sees  with  difficulty  the  outlines  that 
gave  it  form  a;id  expression  during  its  days  of  maturity. 
The  geograprer  and  geologist  in  the  Mt.  Taylor  region, 
however,  find  less  of  interest  in  the  mountain  itself  than 
in  its  surroundings. 

If  we  stand,  says  Dutton,  on  the  eastern  brink  of  the 
Mt.  Taylor  mesa,  the  view  in  the  valley  of  the  Puerco 
to  the  eastward  is  in  some  respects  extraordinary.  The 
edge  of  the  mesa  suddenly  descends  by  a  succession  of 
ledges  and  slopes,  nearly  2000  feet  into  the  rugged  and 


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VoI.rANOKS   Ol"    NoliTII    AMi:i:l<  A. 


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San  Fninclico  I'ecik.  AKtiiIz  I'cAk. 

Fid.  \,    Sdii  Frnncisfo  Mm.iiiaiii,  Aiizmia,  fri>in  the  sinitliwcst.     (»'.  K.  Diittmi.) 


Fia.  B.    Volcanic  ueck  uear  .Mt.  Taylor,  Xew  Moxico.     (I'hotograph  by  U.  S.  Geo- 
logical Survey.) 


mm 


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VOLCANOES    OF    THE    UNITED    STATES 


195 


highly  diversified  valley-plain  below.  The  country  be- 
neath is  a  medley  of  low  cliffs  or  bluffs,  shoving  the 
browns  and  pale  yellows  of  the  Cretaceous  sandstones  and 
shales.  Out  of  this  confused  patchwork  of  bright  colors 
rise  several  objects  of  remarkable  aspect.  They  are  ap- 
parently inaccessible  eyries  of  black  rock  that  rise  from 
800  to  1500  feet  above  the  general  level  of  the  valley. 
The  black  piles,  that  by  contrast  of  form  and  color  make 
such  a  marked  innovation  in  the  scenery  of  the  arid  valley, 
are  the  "necks"  of  ancient  volcanoes.  To  understand 
their  history,  we  must  restore  in  fancy  the  rocks  which 
h" ve  been  carried  away  to  form  the  valley,  and  possibly 
much  more.  Upward  through  the  horizontally  bedded 
rocks,  openings  were  formed  in  some  manner,  but  how  is 
not  fully  known,  and  through  these  openings,  lava  rose 
to  the  surface  and  formed  cones  similar  to  the  scores  of 
cinder  cones  still  to  be  seen  on  the  Mt.  Taylor  mesa, 
and  about  San  Francisco  peak.  How  widely  the  lava 
spread  out  in  sheets  can  only  be  conjectured.  When  the 
eruptions  ceased,  the  lava  slowly  cooled  and  solidified  in 
the  chimneys  through  which  it  came.  Plugs  of  dense  rock, 
many  times  beautifully  columned  on  account  of  shrinkage 
on  cooling,  were  formed,  which  were  far  more  resistant  to 
erosion  than  the  stratified  beds  through  which  they  rose. 
Then  came  a  long  period  of  erosion,  in  the  course  of  which 
many  hundreds  of  feet  of  sedimentary  rock,  and  all  the 
lava  sheets  and  cinder  cohes  which  may  have  rested  upon 
them,  were  swept  away  from  areas  which  aggregate  thou- 
sands of  square  miles.  The  necks  of  resistant  volcanic 
rock  in  the  ancient  chimneys  resisted  waste  and  decay 
much  more  effectually  than  the  softer  beds  of  shale  and 
sandstone  with  which  they  were  surrounded,  and  became 


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VOLCANOES   OP   NORTH   AMERICA 


prominent  landmarks  as  the  general  surface  was  lowered. 
The  leading  outlines  in  this  slow  process  of  dift'erentiai 
erosion  are  simple,  well  understood,  and  similar  to  what 
has  occurred  over  wide  regions  of  the  earth's  surface ;  but 
the  results  produced  are  unusually  striking,  owing  to  the 
bold  relief  of  the  isolated  neck,  the  contrast  of  their 
sombre  precipices  with  the  brightly  colored  desert-valley 
alx)ut  them,  and  the  general  absence  of  vegetation.  The 
time  required  for  the  unearthing  of  the  formerly  buried 
buttes  is  vast,  as  measured  in  years.  The  date  at  which 
the  ancient  volcanoes  were  active  is  placed  by  geologists 
in  the  Tertiary  period  of  the  earth's  history. 

A  view  of  one  of  the  volcanic  necks  de^crib*  r"  above  is 
given  on  Plate  6,  Fig.  B,  and  will  serve  to  show  the  gen- 
eral features  of  scores  of  similar  isolated  piles,  more  or 
less  completely  buried  by  the  products  of  their  own  dis- 
integration and  decay,  that  add  variety  and  interest  to 
the  desolate  region  about  Mt.  Taylor. 

The  completeness  of  the  evidence  by  which  the  history 
just  outlined  is  sustained,  is  shown  by  the  fact  that  the 
volcanic  necks  most  remote  from  the  edge  of  the  mesa 
have  been  completely  exhumed  and  disengaged  from  the 
stratified  beds  that  formerly  surrounded  them,  while  t'i  )se 
nearer  the  mesa  still  have  large  remnants  of  the  end  .  i»  :^ 
strata  around  their  bases  and  mounting  far  up  their  side  ■, 
Nearer  still  to  the  border  of  the  mesa,  the  amount  and 
height  of  the  enclosing  beds  increase,  so  that  only  the 
summits  of  the  necks  protrude.  In  the  wall  of  the  mesa 
itself,  there  are  instances  in  which  the  volcanoes  have 
been  cut  in  two  and  one-half  removed,  so  as  to  expose 
not  only  the  summit  of  the  neck  of  hardened  lava,  but 
a  section  of  the  cinder  cone  that  was  built  above  it.     The 


<^A 


VOLCANOES   OF   THE    UNITED   STATES 


197 


one  or  two  hundred  cinder  cones  on  the  Mt.  Taylor  inesa 
ilkistrate  the  character  of  the  surface  which  has  been  re- 
moved in  tlie  valley  of  the  Puerco,  in  order  to  reveal  the 
volcanic  necks.  The  volcanic  cones  on  the  surface  of  the 
mesa  are  in  various  stages  of  decay,  but  some  of  them 
still  retain  their  craters.  Two  of  them  are  between  800 
and  1000  feet  high,  and  four  or  five  others  are  only  a 
little  smaller.  The  distribution  of  these  vents  upon  the 
mesa  is  very  irregular.  In  some  places  they  are  tliickly 
clustered  together ;  in  others  they  are  separated  by  inter- 
vals of  three  or  four  miles. 

Much  detailed  information  concerning  the  volcanic 
necks  in  the  region  about  Mt.  Taylor  is  given  by  But- 
ton in  the  attractive  report  from  which  the  above  descrip- 
tions are  taken,  and  the  student  who  has  become  interested 
in  their  history  should  consult  the  volume  to  which  refer- 
ence has  been  made. 

In  the  valley  of  Rio  San  Jose,  to  the  south  and  west 
of  the  Mt.  Taylor  plateau,  there  are  lava  flows  with  ex- 
tremely rugged  surfaces,  some  of  which  are  so  recent  that 
time  has  made  no  appreciable  impression  on  them.  These 
lava  flows  are  to  be  seen  from  the  trains  on  the  Atlantic  and 
Pacific  railroad,  near  Laguna,  and  farther  w^estward  from 
McCarty  to  Blue  Water.  Portions  of  this  route  furnish 
typical  examples  of  what  the  Mexicans  term  malpais,  that 
is,  the  rough  surfaces  of  lava  that  have  been  broken  and 
the  blocks  piled  together  in  confused  heaps  as  the  still 
liquid  portion  below  continued  to  flow.  The  glossy 
black  and  exceedingly  rugged  surfaces  of  some  of  the 
lava  coulees  along  the  San  Jos^  are  of  this  type.  In 
other  places  the  corrugated  surfaces  of  slowly  moving 
sheets  which  cooled  without  being  broken  into  blocks, 


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VOLCANOES   OF   NORTH   AMERICA 


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furnish  unmistakable  evidence  of  the  former  liquid  con- 
dition of  the  rock. 

Button  discovered  that  the  vent  from  which  came  the 
lava  in  the  valley  of  Rio  San  Jose,  is  a  low  crater  named 
Tintoro  (the  inkstand)  some  six  miles  north  of  Blue 
Water. 

Ice  Spring  Craters,  Utah. —  About  125  miles  south  of 
Salt  Lake  City  and  well  out  in  the  desert-valley  to  the 
west  of  the  bold  Wasatch  Mountains,  there  are  several 
craters  which  derive  special  interest  from  their  associa- 
tion with  the  history  of  an  ancient  lake  which  once 
flo(jded  many  of  the  now  arid  valleys  of  Utah.  The  old 
lake  referred  to,  named  Lake  Bonneville,'  was  in  exist- 
ence during  the  Pleistocene  period  of  geological  history; 
the  time  that  witnessed  various  advances  and  retreats  of 
glacial  ice  over  the  northern  portions  of  North  America. 
Some  of  the  volcanoes  in  the  valleys  of  Utah  are  of  more 
ancient  date  than  the  first  rise  of  Lake  Bonneville ;  at 
least  one  of  them  had  a  period  of  activity  during  the  time 
the  lake  basin  was  flooded,  and  several  small  examples, 
which  form  a  compact  group  known  as  the  Ice  Spring 
craters,  have  come  into  existence  since  the  water  of  the 
old  lake  disappeared. 

The  Ice  Spring  craters  (Plate  7)  are  situated  on  a  broad 
featureless  plain  composed  of  the  sediments  of  Lake  Bonne- 
ville, known  as  the  Sevier  Desert,  and  are  ten  miles  north- 
west of  the  town  of  Fillmore. 

At  the  locality  mentioned,  there  are  three  small  craters 
of  scoria  and  lapilli,  which  are  fresh  in  appearance  and 

^  A  report  on  Lake  Bonneville  by  G.  K.  Gilbert,  forms  Monograph,  Vol.  I 
of  the  U.  S.  Geological  Survey.  The  craters  mentioned  are  described  on 
pp.  319-339  of  this  report. 


^4 


VOLCANOES   OF   THE    UNITED   STATES 


199 


nearly  perfect  in  form.  Closely  associated  with  these 
and  partially  concealed  by  them,  are  fragments  of  at  least 
nine  other  craters  of  similar  character.  About  this  group 
of  volcanic  vents  there  are  coulees  of  basaltic  lava  which 
flowed  from  them  at  various  times  and  cover  an  area  of 
12.5  square  miles. 

A  bird's-eye  view  of  the  three  well-preserved  craters 
and  a  fragment  of  a  much  larger  one  named  the  Crescent, 
as  well  as  of  the  lava  field  to  the  eastward  of  the  group, 
is  shown  in  Plate  7.  This  view  here  reproduced  from 
Gilbert's  monograph,  was  constructed  from  sketches,  with 
the  aid  of  an  accurate  plane-table  map,  and  will  serve  bet- 
ter than  a  written  description  to  convey  an  idea  of  the 
leading  features  of  the  central  portion  of  the  Ice  Spring 
craters. 

The  Crescent,  as  just  stated,  is  only  a  fragment  of  the 
crater  wall  of  a  volcano  which  has  been  more  than  half 
destroyed  by  explosions.  In  some  respects  it  is  to  be 
compared  to  the  rim  of  ancient  date  that  partially  sur- 
rounds Vesuvius,  and  known  as  Mt.  Somma.  The 
Crescent  rises  250  feet  above  its  eastern  base,  and  when 
complete  must  have  had  a  diameter  of  about  2200  feet. 

The  central  crater  shown  in  the  illustration,  named  the 
Miter,  is  probably  the  most  recent  of  the  group,  as  no 
other  crater  overlaps  it.  It  rises  250  feet  above  its  west 
base  and  275  feet  above  the  bottom  of  the  pit  it  encloses. 
Its  rim  is  nearly  circular,  and  has  a  diameter  of  950  feet. 
After  it  had  reached  approximately  its  present  size,  lava 
rose  within  it  and,  breaking  through  its  north  side,  flowed 
away  as  a  well-defined  stream,  which  expanded  on  the  adja- 
cent plain.  This  lava  eruption  was  followed  by  one  of 
explosive  violence,  during  which  the  break  in  the  crater 


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200 


VOLCANOES   OF   NORTH   AMERICA 


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rim  was  repaired  by  the  deposition  of  scoriaceous  lapilli. 
The  lava  again  rose  in  the  crater,  and  again  broke  tlirough 
its  wall,  this  time  discharging  westward,  leaving  a  breach 
the  bottom  of  which  is  seventy-five  feet  higher  than  the 
crater's  bottom. 

Between  the  Miter  and  the  Crescent  is  a  low  cinder 
cone,  resembling  the  Miter  in  shape,  but  only  400  feet 
in  diameter,  named  Terrace  crater,  which  is  well  within 
the  area  formerly  embraced  by  the  Crescent. 

The  v/alls  of  Terrace  crater,  as  described  by  Gilbert, 
are  for  the  most  part  low  and  characterized  by  a  gentle 
outward  slope.  At  their  culminating  point  they  are 
scoriaceous,  but  elsewhere  they  are  of  relatively  com- 
pact lava,  with  a  rude  stratification,  as  though  formed 
by  the  addition  of  successive  sheets.  Its  formation  was 
evidently  attended  by  very  little  explosive  action,  and 
there  is  some  ground  for  believing  that  its  cavity  was 
produced  by  the  fusion  of  scoriaceous  matter,  the  product 
of  some  earlier  eruption.  Its  outline  is  irregular,  with 
an  extreme  length  of  1100  feet  and  a  width  of  700  feet. 
At  one  stage  in  its  history  it  was  occupied  by  a  molten 
lake  about  fourteen  acres  in  extent,  and  the  partial  con- 
gelation of  the  surface  of  this  lake  left  a  terrace  at  one 
margin.  The  subsequent  history  of  the  crater  includes 
the  formation  of  four  narrow  terraces  at  lower  levels. 
The  first  lowering  of  the  molten  lake  appears  to  have 
been  accomplished  by  the  breaking  of  the  crater  wall 
at  the  south,  and  a  consequent  outflow.  The  subsequent 
lowerings  were  caused  by  the  retreat  of  the  lava  down 
the  conduit  by  which  it  had  originally  entered  the  crater 
from  beneath.  This  conduit  remains  open  and  can  be 
explored   for  twenty-five  feet,  when  progress  is  stopped 


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VOLCANOES   OF    THE    I'NITED   STATES 


201 


by  water.  It  is  a  circular  tube  twelve  feet  in  diameter, 
and  inclined  ten  or  fifteen  degrees  from  the  vertical. 
Tlie  stony,  arrested  drops  still  pendent  from  its  sides 
testify  by  their  small  diameter  to  the  high  fluidity  of 
the  lava.  The  depth  of  the  crater  below  its  general 
rim  is  260  feet,  below  the  sill  of  its  last  outflow  220  feet, 
and  below  the  scoriaceous  crag  that  overlooks  it  on  one 
side  350  feet. 

The  streams  of  basalt  flowing  from  the  Ice  Spring 
craters  —  still  quoting  Gilbert  —  have  formed  two  con- 
fluent fields,  the  first  extending  three  and  one-half  miles 
northward,  with  a  general  breadth  of  two  miles,  the 
second  three  and  one-quarter  miles  westward,  with  a 
general  breadth  of  one  and  one-half  miles.  Their  area 
is  approximately  twelve  and  one-half  square  miles. 
Their  marginal  depth  will  average  about  thirty  feet,  and 
their  mean  depth  is  estimated  at  fifty  feet.  The  volume 
of  the  ejected  material  is  approximately  one-eighth  of  a 
cubic  mile.  The  lava  is  black  or  dark  gray  basalt,  with 
exceedingly  rough  surfaces,  due  to  the  breaking  of  the 
crust  as  the  still  plastic  portion  beneath  continued  to 
flow.  In  places  the  surface  blocks  are  piled  in  confused 
wave-like  ridges,  whose  crests  are  twenty  or  thirty  feet 
above  their  troughs. 

One  curious  feature  of  the  lava  streams  that  flowed 
from  the  Ice  Spring  craters  and  fed  the  surrounding 
coulee,  is  that  near  the  craters  they  are  depressed  fifteen 
or  twenty  feet  below  the  adjacent  surface.  The  appear- 
ance is  as  if  the  streams  of  molten  rock  had  eroded 
channels  for  themselves.  Yet,  as  stated  by  Gilbert,  the 
adjacent  surfaces  resemble  very  closely  the  surfaces  of 
the  streams.     "  The  explanation  appears  to  be  that  each 


1] 


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202 


VOLCANOES   OF    NORTH    AMEllirA 


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of  these  outpourings  varied  in  volume,  now  swelling, 
now  sinking.  When  most  copious,  it  spread  beyond  its 
channel  like  an  ac^ueous  stream  and  deposited,  not  its 
sediment,  but  its  crust.  The  walla  of  the  channels  dis- 
play a  conformatory  stratification." 

Tabernacle  Crater  and  Lava  Field,  Utah.  —  Four  miles 
south  of  the  Ice  Spring  craters,  there  is  another  volcano 
more  recent  than  the  withdrawal  of  the  water  of  Lake 
Bonneville,  and  named  Tabernacle  crater  in  reference  to 
its  resemblance,  when  seen  from  a  distance  of  a  mile  or 
two,  to  the  great  assembly  building  in  Salt  Lake  City, 
known  as  the  Tabernacle. 

Tabernacle  crater  is  composed  of  the  same  varieties  of 
basalt  as  the  Ice  Spring  crater,  and  has  two  crater  rims, 
one  within  the  other.  Surrounding  the  crater  is  a  nearly 
circular  lava  field  about  three  miles  in  diameter,  with 
an  area  of  approximately  seven  square  miles.  The 
point  of  issue  is  not  central,  but  lies  near  the  southeast 
margin  of  the  lava  coulee. 

The  outer  rim  of  the  crater,  one-third  of  which  has 
been  removed,  has  a  diameter  of  2200  feet  and  on  the 
highest  side  rises  120  feet  above  the  surrounding  lava 
fields.  The  inner  rim,  composed  of  scoriaceous  material, 
is  complete  in  general  form,  but  is  rough  and  abounds  in 
pinnacles. 

The  chief  phases  in  the  history  of  Tabernacle  crater, 
as  determined  by  Gilbert,^  are  as  follows :  When  Lake 
Bonneville  stood  at  a  comparatively  low  level,  known 
as  the  Provo  stage,  it  has  a  depth  of  from  fifty  to  seventy- 
five  feet  above  the  valley  bottom  where  the  crater  now 


^"Lake  Bonneville,"  U.  S.  Geological  Survey,  Monograph,  Vol.  I,  pp.  329- 


332. 


:i 


VOLCANOES    OF   THE    I'NITED   .STATES 


203 


stands,  and  was  held  at  a  constant  level  for  many  centu- 
ries. An  explosive  eru})ti()n  occurred  beneath  the  lake, 
of  such  violence  that  the  material  hhnvn  out  was 
deposited  most  abundantly  at  a  distance  of  more  than 
a  thousand  feet  from  the  point  of  discharge.  The  rim 
built  up  by  this  explosive  eruption  eventually  rose  above 
the  surface  of  the  lake  and  shut  out  its  waters.  The 
eruption  then  became  less  violent,  and  the  material 
discharged  changed,  becoming  pasty.  (^uiet  eruptions 
followed,  developing  a  low  black  iisland  which  had  a 
line  traced  about  it  by  the  waves  before  the  lake  was 
finally  lowered  by  evaporation.  The  declining  phase  of 
the  eruption  was  again  explosive. 

The  lava  field  about  Tabernacle  crater  terminates  in 
most  directions  in  a  steep  cliff,  showing  that  the  lava 
flowed  sluggishly,  and  was  of  such  consistency  as  to  form 
a  deep  stream  instead  of  spreading  widely  and  ending  in 
a  thin  edge,  as  is  the  habit  of  very  liquid  lavas.  The 
surface  is  rugged,  on  account  of  the  breaking  of  the  crust 
by  the  motion  of  the  still  liquid  portion  beneath.  The 
sinking  of  the  blocks  formed  by  the  breaking  of  the 
crust  into  the  plastic  lava,  may  have  increased  the  fric- 
tion of  flow,  and  thus  caused  the  flood  to  advance  with  a 
precipitous  terminus.  The  height  of  the  outer  escarp- 
ment is  in  places  sixty-five  feet. 

Among  the  minor  points  oi  interest  to  the  student  of 
volcanic  phenomena  at  the  Ice  Spring  and  Tabernacle  cra- 
ters, is  the  presence  of  lapilli  w  idely  scattered  on  the  lava 
flow,  showing  the  violence  with  which  the  fragments  were 
thrown  out,  although  there  is  an  absence  of  evidence 
showing  excessive  energy.  Near  the  craters  much  of  the 
scoria  was  ejected  in  a  pasty  condition  and  came  to  rest 


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204 


VOLCANOKH   OF   NOUTII    AMKUICA 


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wliilu  Htill  plastic.  Some  of  the  bombs  tiro  possibly  a 
mile  from  the  crater  from  which  they  started  on  their 
aerial  journey,  but  struck  the  ground  while  still  plastic, 
and  were  flattened  so  as  to  form  cakes,  in  some  instances 
between  two  and  three  feet  in  diameter;  on  the  under 
side  they  preserve  impressions  of  the  rough  surfaces  on 
which  they  fell.  Well-formed  spherical  bombs,  charac- 
teristic of  many  volcanic  regions,  which  cool  during  their 
passage  through  the  air  and  sometimes  exhibit  a  si)iral 
twist  due  to  rotation  while  still  plastic,  were  not  noticed. 

The  surfaces  of  some  of  the  lava  Hows,  particularly  in 
the  neighborhood  of  the  Miter,  are  exceedingly  rugged, 
on  account,  as  already  mentioned,  of  the  breaking  of  the 
crust  formed  on  the  surface,  while  the  still  plastic  portion 
below  continued  to  flow.  The  rough  surfaces  thus  pro- 
duced are  of  the  same  character  as  the  fields  of  the 
Hawaiian  islands.  Tn  some  instances  about  the  Ice 
Spring  craters,  especially,  the  under  surface  of  the  angu- 
lar blocks  formed  by  the  breaking  of  the  crust  are 
grooved  and  striated  in  a  striking  manner,  and  show  the 
effect  of  the  friction  of  the  moving  undercurrent  while 
the  crust  was  yet  plastic  at  a  depth  of  eight  or  ten  inches 
below  the  exposed  surface. 

The  interstices  of  the  lava  in  the  coulee  about  Taber- 
nacle crater  are  in  some  places  filled  Avith  fine,  yellowish 
dust,  wdiich  has  gained  access  to  steam  cavities,  through 
openings  too  small  to  be  distinguished  by  the  eye. 

While  the  Ice  Spring  and  Tabernacle  craters  are  young 
as  compared  with  the  fall  of  the  water  of  Lake  Bonne- 
ville below  the  lowest  notch  in  the  rim  of  the  basin  that 
confined  it,  yet  their  absolute  age  in  years  cannot  be 
determined.     The  lavas  are  fresh  in  appearance,  and  no- 


VOLCANOES  OF  THE   UNITED  STATES 


205 


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where  have  yicjldoJ  to  tlio  action  of  the  atmosphere  so  as 
to  form  a  soil.  It  is  to  be  reiuem))ure(l,  however,  that 
under  the  dry  eiimate  of  Utah,  such  a  change  is  exces- 
sively slow,  and  tlie  fresh  appearance  of  the  lava  is  not 
an  argument  in  lavor  of  very  recent  origin. 

In  the  same  valley  with  the  volcanoes  just  described, 
there  is  another  of  older  date,  named  Pavant  butte, 
about  which  the  waters  of  Lake  Doinieville  left  conspicu- 
ous markings.  This  volcanic  pile  is  formed  of  lapilli, 
and  furnishes  evidence  that  an  eruption  took  place  when 
the  lake  was  at  its  highest  stage,  and  beneath  a  body  of 
water  350  feet  deep.  The  resulting  cone  was  built  not 
only  to  the  surface  of  the  water,  but  450  feet  higher. 
Eruption  ceased  with  the  fall  of  the  water  and  has  not 
since  been  renamed.  A  detailed  and  instructive  account  of 
this  volcano  may  be  found  in  the  report  on  Lake  Bonne- 
ville, already  referred  to. 

Craters  near  Ragtown,  Nevada.  —  The  craters  in  Utah, 
just  described,  derive  much  of  their  interest,  as  has  been 
seen,  from  their  association  with  the  history  of  Lake  Bonne- 
ville. In  Nevada  there  was  another  great  lake  in  Pleisto- 
cene times,  contemporary  with  the  one  in  Utah,  which  is 
known  as  Lake  Lahontan.  The  Nevada  lake  also  had 
volcanic  phenomena  associated  with  its  history. 

One  of  the  broadest  portions  of  Lake  Lahontan  occu- 
pied what  is  now  the  Carson  desert,  Nevada.  On  the  inner 
slopes  of  the  mountains  surrounding  and  nearly  enclosing 
this  basin,  there  are  shore  lines  which  show  that  at  one  time 
it  was  flooded  to  the  depth  of  500  feet  above  the  stratified 
clays  now  forming  its  floor.  In  the  western  part  of  the 
desert,  about  two  miles  from  a  little  settlement  named 
Ragtown,  and  twenty-two  miles  southeast  of  Wadsworth, 


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20G 


VOLCANOES   OF    NORTH   AMERICA 


a  town  oil  the  Central  Pacific  railroad,  there  are  two  circu- 
lar depressions  occupied  by  strongly  alkaline  water,  which 
are  termed  the  Ragtown  ponds,  or  Soda  lakes. 

These  lakes  occupy  volcanic  craters  the  rims  of  which 
rise  above  the  surface  of  the  surrounding  sage-brusL-covered 
desert,  while  their  bottoms  are  depressed  below  that  hori- 
zon. The  rim  of  the  larger  crater,  at  its  highest  point,  is 
80  feet  above  the  desert  and  165  feet  above  the  surface 
of  the  water  within.  The  water  has  a  maximum  depth  of 
147  feet,  making  the  total  depth  of  the  crater  312  feet. 
Its  bottom  is  232  feet  below  the  desert's  surface.  The  least 
diameter  of  the  crater  at  the  water's  surface  is  3168  feet, 
and  its  greatest  diameter  4224  feet.  The  area  of  the  lake 
is  268.5  acres.  The  diameter  of  the  crater,  measured  from 
opposite  points  on  the  summit  of  its  rim,  might  be  vari- 
ously determined,  owing  to  the  lack  of  a  well-defined  crest 
at  all  places,  but  in  general  is  about  one  mile.  The 
smaller  lake  is  much  inferior  to  its  companion  in  all  di- 
mensions. Its  diameter  from  points  on  opposite  sides  of 
its  low  and  not  well-defined  rim,  is  about  one-half  mile, 
and  its  depth  to  the  shallow  pond  within,  approximately 
seventy  feet. 

The  measurements  just  given  show  that  the  larger 
crater  is  by  no  ineans  insignificant.  The  proof  that  it 
was  produced  by  volcanic  explosions,  and  also  its  place 
in  the  history  of  Lake  Lahontan,  is  shown  by  the  fol- 
lowing evidence.  The  general  form  of  the  crater,  that 
is,  a  depression  surrounded  by  a  raised  rim,  is  such  as 
frequently  results  from  the  blowing  out  of  projectiles 
when  volcanoes  of  the  explosive  type  are  in  action. 
Sections  of  the  wall  of  the  crater  show  that  it  is  com- 
posed of  lapilli  and  volcanic  dust,  together  with  numerous 


T-^f-rf.rTrtrwi'rc 


M 


VOLCANOES   OP   THE   UNITED   STATES 


20i 


'  I  U 


scoriaceous  fragments  of  basalt.  The  basaltic  masses 
are  of  all  sizes  up  to  two  feet  in  diameter,  and  occur  at 
all  heights  in  the  crater's  walls  from  base  to  summit,  and 
on  the  adjacent  surface  of  the  desert.  Frequently,  in  the 
case  of  freshly  exposed  basaltic  masses  in  the  crater  walls, 
the  strata  of  fine,  loose  material  on  which  they  rest  are 
beat  down  in  the  manner  that  would  be  expected  had  the 
"  bombs  '  been  thrown  into  the  air  and  fallen  to  their 
present  position  from  a  height  of  several  hundred  feet. 
The  layers  of  lapilli  forming  the  crater's  rim  are  fre- 
quently inclined  both  in  the  direction  of  its  outer  and 
inner  slopes,  and  are  also  frequently  interrupted  or  uncon- 
formable, portions  of  the  deposit  having  been  removed, 
as  is  common  in  the  case  of  craters  that  have  been  par- 
tially destroyed  by  the  violence  of  the  explosions  from 
within,  and  subsequently  rebuilt. 

Interstratified  with  the  layers  of  volcanic  origin  are 
beds  of  lacustral  clay  and  deposits  of  calcareous  tufa. 
The  tufa  is  identical  in  origin,  so  far  as  one  can  judge, 
with  extensive  sheets  of  the  same  character  occurring  at 
numerous  localities  throughout  the  Lahontan  basin,  and 
determined  to  have  been  precipitated  from  the  waters  of 
the  former  lake.  The  evidence  is  clear  that  the  volcanoes 
whose  craters  are  now  occupied  by  the  Soda  lakes,  were  in 
activity  during  the  existence  of  Lake  Lahontan,  and  also 
that  the  last  eruption  occurred  since  the  lake  waters  fell 
below  the  level  of  the  Carson  desert.  The  outer  slopes  of 
the  crater  walls  are  not  marked  by  terraces,  as  would  have 
been  the  case  had  such  piles  of  loose,  incoherent  material 
been  3xpo::ed  to  wave  action.  The  volcanoes  were  of  the 
explosive  type  and  threw  out  only  fragmental  material. 
No  lava  streams  are  associated  with  them. 


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'  tMvn  w^'lli:)^w\    '■  !■■  I  '  .^-.Uiy."!"  I'y.j^JW 


208 


VOLCANOES   OF   NORTH   AMERICA 


i  '     ,\ 


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Mi 


The  Soda  lakes  are  the  basis  of  a  considerable  soda 
industry  and  are  of  interest  also  on  account  of  the  crus- 
taceans and  insects  that  live  in  their  waters.  In  the 
larger  lake,  crystals  of  a  pure  white  soda  mineral  named 
gatjlussite,  are  forming.  The  composition  of  the  waters 
of  these  lakes  and  other  facts  concerning  their  history  are 
given  in  the  books  mentioned  in  the  following  foot-note.^ 

Volcanoes  of  Mono  Valley,  California.  —  Mono  valley 
is  situated  at  the  eastern  base  of  the  Sierra  Nevada,  in 
about  the  centre  of  the  eastern  border  of  California,  but 
extends  across  the  interstate  boundary  into  Nevada.  In 
the  lowest  part  of  the  valley  and  reaching  the  base  of 
the  steep  eastern  slope  of  the  Sierra  Nevada  lies  Mono 
Lake,  a  body  of  intensely  alkaline  water. 

The  eastern  portion  of  Mono  valley  partakes  of  the 
desert-like  character  of  the  great  interioi  arid  region  of 
which  it  is  a  part ;  but  its  western  and  southwestern  por- 
tion is  well  watered  by  streams  which  have  their  sources 
in  the  forest-covered  Sierra  Nevada.  Like  many  other 
enclosed  basins  between  the  Sierra  Nevada  and  Rocky 
Mountains,  Mono  valley  has  an  instructive  history  of 
climate  fluctuations,  in  the  form  of  terraces,  lacustral 
deposits,  glacial  moraines,  etc.,  written  on  its  inner 
slopes,  but  at  present  we  must  pass  this  by. 

In  the  centre  of  the  lake  at  the  present  time  there  are 
two  islands,  named  Paoha  and  Negit  islands,  besides  sev- 
eral rocky  crags.  We  will  begin  our  studies  of  the  instruc- 
tive volcanic  phenomena  of  Mono  valley  by  examining  these 
islands.     Let  the  reader  in  fancy  take  a  seat  beside  me  in 

1  Arnold  Hague  and  S.  F.  Emmons,  U.  S.  Geological  Survey  of  the  I  orti- 
eth  Parallel,  Vol.  II,  1877,  pp.  744-750.  Clarence  King,  U.  S.  Geological  Sur- 
vey of  the  Fortieth  Parallel,  Vol.  I,  1878,  pp.  510-514.  I.  C.  Russell,  "  Lake 
Lahontan,"  U.  S.  Geological  Survey,  Monograph,  Vol.  XI,  1885,  pp.  76-PO. 


.1\ 


VOLCANOES   OF  THE   UNITED   STATES 


209 


i 


a  small  boat,  with  a  single  Indian  from  the  encampment 
on  the  shore  to  use  the  paddle,  and  I  will  endeavor  to 
point  out  some  of  th  ^  more  instructive  features  that  pre- 
sent themselves  as  we  glide  over  the  placid  surface  of  the 
lake,  on  our  way  to  the  islands. 

The  water  over  which  we  pass  gives  the  fingers  a  slip- 
pery feeling ;  if  we  taste  it  we  find  that  it  is  intensely 
alkaline  and  ])itter.  As  we  look  down  into  the  water  we 
see  that  it  is  clear  and  limpid^  but  the  view  is  usually 
obstructed  by  countless  numbers  of  brine  shrimps  {Artc- 
mia)  and  the  larvce  of  flies.  The  lavae  are  thrown  ashore 
by  the  waves  in  windrows  that  are  frequently  a  foot  or 
more  deep.  The  lava  cases  on  drying  are  detached  from 
the  dried  worms  within  and  may  be  easily  separated 
On  the  sloping  sandy  shore  near  an  encampment,  you 
may  see  a  number  of  Indian  women  with  large  conical 
baskets  on  their  backs,  and  a  second  shallow  paddle- 
shaped  basket  in  their  hands.  With  the  flat  basket  they 
throw  the  dried  larvae  in  the  air  and  allow  the  w^ind  to 
carry  away  the  chaff-like  cases.  The  desiccated  worms 
are  then  transferred  to  the  baskets  on  their  backs,  to  be 
used  as  food. 

On  the  borders  of  the  valley  we  can  see  the  horizontal 
lines  at  various  heights  that  mark  the  level  of  the  w^ater 
in  former  times.  The  highest  of  these  lines,  wdiich  is 
drawn  about  the  steep  faces  of  outstanding  bluffs  and 
continued  into  the  lateral  valleys  between,  is  675  feet 
above  the  present  lake  surface,  but  is  not  now  perfectly 
horizontal.  A  movement  in  the  rocks  has  taken  place 
since  the  lake  was  at  its  highest  stage.  The  differences 
in  elevation  at  various  points  in  the  old  beach  line,  how- 
ever, are  not  over  fifteen  or  tw^ntv  feet. 


'■A 
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210 


VOLCANOES   OF   NOUTH    AMERICA 


The  scene  that  invites  the  attention  of  tlie  traveller  in 
Mono  valley  to  the  exclusion,  for  a  time  at  least,  of  all 
other  features,  is  the  range  of  niagnilicent  mountains  that 
limits  the  view  to  the  southwest.  The  surface  of  the  lake 
is  G380  feet  above  the  sea.  The  highest  of  the  serrate 
peaks,  Mt.  Dana,  rising  precipitously  from  its  border, 
reaches  G612  feet  above  us,  and  is  12,992  feet  above 
the  sea.  Twelve  miles  south  of  Mt.  Dana  and  also  on 
the  rim  of  the  basin  surrounding  Mono  Lake,  stands  Mt. 
Lyell,  13,042  feet  in  height,  amid  a  group  of  white  cathe- 
dral-like spires  that  are  but  little  inferior  to  it  in  eleva- 
tion. On  the  northern  sides  of  several  of  the  '.igher 
peaks  in  view  there  are  small  glaciers,  which  contribute 
the  water  formed  by  their  melting  to  the  swift  streams 
supplying  Mono  Lake.  In  the  deep  gorges  excavated  in 
the  sides  of  the  mountains  we  can  distinguish  the  rounded 
contours  of  the  valleys  due  to  the  broadening  and  smooth- 
ing of  stream-cut  valleys  by  ancient  glaciers.  When  the 
gorges  open  out  into  the  plain  bordering  the  lake,  they 
are  conspicuous  moraines,  which  in  several  instances  are 
prolonged  from  the  entrances  of  the  high  grade-valley,  as 
parallel  morainal  embankments,  more  than  a  thousand  feet 
high,  which  were  deposited  on  the  Ijorder  of  the  ancient 
glaciers  after  escaping  from  the  confinement  of  the  moun- 
tain precipices. 

To  the  south  of  the  lake,  and  separated  from  the  rugged 
eastern  face  of  the  Sierra  Nevada  by  an  extension  of  Mono 
valley,  rises  a  conspicuous  range  of  volcanoes  which  fur- 
nish some  of  the  most  pleasing  and  instructive  features  in 
the  diversified  landscape.  These  volcanoes  are  known  as 
the  Mono  craters,  and  will  be  examined  after  our  visit 
to  the  islands  which  in  fancy  we  are  nearing. 


^) 


VOLCANOES   OF    Till-:    I'MTED   STATES 


211 


The  larger  of  tlie  two  main  islands  is  mild  in  relief  and 
alnKJst  white  in  color,  while  the  smaller  one  is  rugged  and 
nearly  l)lack.  These  diii'erences  have  an  intimate  connec- 
tion with  their  origin  and  geological  history.  In  seeking 
for  a  name  hy  which  to  designate  the  islands,  during  my 
exploration  of  Mono  valley,  it  was  suggested  that  their 
contrasts  in  color  might  he  used,  hut  1  preferred  to  record 
some  of  the  poetic  words  in  the  language  of  the  ahorigines 
who  still  inhalnt  the  valley.  On  the  larger  island  there 
are  hot  springs  and  orifices  through  which  heated  vapors 
escape.  These  hot  springs  and  fumaroles  are  the  linger- 
mg  remnants  of  V(jk'anic  energy  which,  in  times  not 
remote,  built  some  of  the  most  conspicuous  landmarks 
in  the  valley.  It  seems  fitting  that  the  words  of  the 
Pa-vi-o-osi  people,  who,  like  the  volcanic  energy,  are  fast 
passing  away,  should  be  attached  to  the  scenes  with  which 
they  have  long  been  familiar.  Among  the  legends  of  the 
aborigines  there  is  one  concerning  diminutive  sprites  hav- 
ing long,  waving  hair,  that  were  sonietimes  seen  in  the 
vapor-wreaths  escaping  from  the  hot  springs.  The  word 
Pa-o-ha,  by  which  these  elves  were  known,  is  also  used 
to  distinguish  the  hot  springs  themselves.  We  therefore 
named  the  larger  island  in  memory  of  the  children  of  the 
mist  that  hold  their  revels  there  on  moonlit  nights,  Paolia 
Island. 

The  island  near  Paoha  Island,  and  second  to  it  in  size, 
has  been  called  Negit  Island,  Negit  being  the  Pa-vi-o-osi 
name  of  the  blue-winged  goose. 

On  reaching  Paoha  Island,  we  find  shelter  for  our  boat 
in  a  cove  on  its  eastern  side,  which  we  recognize  at  once 
as  being  a  partially  submerged  crater  of  basaltic  lapilli. 
The  side  of  the  crater  facing  the  lake  has  been  broken 


if    if 


V 


212 


VOLCANOES   OF   NORTH   AMEllICA 


i   (  ' 


/ '  , 


II  I. 


:■   h'' 


\i 


down,  and  the  lake  water  now  extends  into  the  cavity 
kept  open  at  the  time  the  crater  was  formed  by  tiie  vio- 
lently escaping  steam. 

On  walking  over  Paoha  Island,  we  find  tliat  the  white- 
ness of  its  surface,  which  we  noted  on  approaching,  is  due 
to  a  thick  deposit  of  lacustral  clay  and  marl,  together 
with  considerable  quantities  of  volcanic  dust,  which  was 
showered  down  on  the  lake  when  its  surface  was  consider- 
ably higher  than  at  present  and  the  island  Avas  completely 
submerged.  On  the  surface  of  the  lake  beds  and  evi- 
dently dropped  there  since  the  island  was  left  exposed 
by  the  recession  of  the  lake,  we  find  masses  of  scoriaceous 
basalt,  which  become  more  and  more  numerous  as  we 
approach  an  elevation  on  the  northeast  extremity  of  the 
island  and  only  a  quarter  of  a  mile  north  of  the  cove  in 
which  we  landed.  Mingled  with  the  blocks  of  basalt  are 
numerous  rounded  and  water-worn  pebbles  of  granite  and 
other  rocks,  which  one  familiar  with  the  geology  of  the 
Sierra  Nevada  will  at  once  recognize  as  being  similar  to 
the  rocks  there  exposed  and  identical  with  the  pebbles  in 
the  streams  that  flow  from  the  mountains.  As  these  peb- 
bles, like  the  blocks  of  volcanic  rock  with  which  they  are 
mingled,  do  not  occur  in  the  lacustral  sediments,  so  far  as 
we  can  discover,  it  is  evident  that  they  reached  their  pres- 
ent resting-place  at  a  recent  date.  Since  the  pebbles  are 
not  covered  by  lake  sediments  but  rest  on  them,  they 
must  have  been  brought  since  the  island  eme.ged  from 
the  water.  Without  going  over  all  the  steps  in  the  evi- 
dence by  which  an  explanation  of  the  presence'  of  the 
pebbles  was  reached,  I  may  say  that  in  company  with 
the  blocks  of  basalt  and  much  lapilli  and  dust  associated 
with   them,  they  were   blown   out   of   a   crater   on   the 


VOLCANOES   OF  THE   UNITED  STATES 


213 


island,  and  fell  on  the  adjacent  surface  at  a  recent  date. 
The  crater  from  which  they  came  forms  the  hill  already 
mentioned,  on  the  northeast  point  of  the  island.  A  map 
of  this  locality,  including  also  the  partially  submerged 
crater  in  which  we  left  our  boat,  is  given  below. 

In  further  explanation  of  the  presence  of  the  pebbles 
referred  to,  I  may  say  that  similar  water-worn  rocks 
occur  on  the  neighboring  Mono  craters  even  to  their 
summits.     Previous  to  the  origin  of  Mono  Lake  or  dur- 


\.  A 


K    E 


Fui.  7.    North  end  of  Paolia  Island,  Mono  Lake,  Cal.     (Surveyed  by  W.  D.  Johnson.) 

ing  a  period  of  low  water  in  its  earlier  history,  the  streams 
from  the  mountains  spread  a  sheet  of  gravel  over  the 
valley.  The  volcanic  vents  were  opened  through  this 
deposit,  and  the  violence  with  which  steam  escaped, 
carried  the  stones  upwards  in  much  the  same  manner  that 
volcanic  bombs  are  projected  out  of  volcanic  vents,  and 
scattered  them  over  the  adjacent  region.  These  pebbles 
of  granite  are  similar,  so  far  as  their  connection  with  the 
volcanoes  of  Mono  valley  is  concerned,  with  the  blocks  of 
limestone   thrown   out   by  Vesuvuis.     At    Vesuvius    the 


!l 


''I 


,  '^  I 


214 


VOLCAN'OKS    (»K    NOUTII    AMEUK'A 


iM'i 


rw' 


volcanic  conduit  traverses  liin' stones,  portions  of  which 
are  torn  off  by  the  violent  uprush  of  steam  or  forced  into 
the  conduit  Ijy  steam  explosions  from  its  sides ;  in  Mono 
valley  the  volcanoes  opened  conduits  througli  a  stratum 
of  gravel  and  rounded  boulders,  some  of  which  were 
carried  to  the  surface  with  such  violence  that  they  were 
projected  high  in  the  air,  and  fell  about  the  craters. 

Each  of  the  bowl-shaped  depressions  shown  in  the 
accompanying  sketch-map  is  a  crater  of  recent  date. 
They  do  not  contain  lacustral  clays  and  are  not  scored 
with  beach  lines  on  their  outer  slopes.  The  loose  inco- 
herent nature  of  liie  material  of  which  they  are  composed 
renders  it  evident  that  they  could  not  have  withstood  the 
action  of  w^aves  and  currents  for  even  a  Ijrief  period  with- 
out having  evidence  of  the  fact  inscribed  upon  them. 
They  are,  therefore,  more  recent  than  the  last  high-water 
stage  of  Mono  Lake. 

The  largest  crater  is  from  150  to  175  feet  deep.  The 
regularity  of  its  outlines  has  been  broken  by  the  formation 
of  two  smaller  craters  on  its  rim.  The  narrow  ridge  of 
lapilli  separating  the  main  crater  from  its  larger  parasite, 
forms  a  symmetrical  curve,  as  it  descends  from  one  end  of 
the  broken  rim  of  the  older  crater  and  ascends  to  the  oppo- 
site extremity.  The  craters  separated  by  the  low  wall 
hold  lakelets  of  strongly  alkaline  water,  whose  surfaces  are 
on  a  level  with  Mono  Lake,  from  which  they  are  supplied 
by  percolation.  The  waves  of  the  surrounding  lake  have 
carved  away  the  base  of  the  outoi"  slope  of  the  crater  on 
the  north  and  east,  and  made  it  precipitous,  and  will  no 
douljt  soon  open  breaches  through  it.  so  that  the  lake- 
lets will  have  open  connections  with  the  surrounding 
w^aters.     A    submerged   crater   a   few   rods    from    shore, 


.■■*-t.  .■•-i.'-i,Au',.>  1. 


VOLCANOES    OF   THK    LNITKI)   STATES 


21  r, 


revealed  )>}'  soundings,  shows  that  one  nieniljer  of  the 
group  has  perhaps  already  succumbed  to  the  attack  of 
the  waves,  or  else  was  formed  by  explosions  beneath  the 
lake's  surface. 

On  the  west  side  of  the  craters  described  above,  there 
is  a  small  lava  flow,  also  shown  in  Fig.  7,  which  descends 
into  the  lake.  That  this  lava  stream  was  formed  at  a 
recent  date  is  at  once  suggested  by  the  fresh  appearance 
of  the  black,  angular  blocks  composing  it.  The  lava  is 
not  covered  with  lacustral  sediments,  and  is  without  cer- 
tain calcareous  incrustations,  which  are  common  on  simi- 
lar rocks  in  various  parts  of  the  valley  below  the  ancient 
beach  lines  that  record  the  former  horizons  of  the  lake's 
surface.  The  lava  flow  is,  therefore,  more  recent  than  the 
latest  high-water  stage  of  the  lake.  It  is  also  of  more 
recent  origin  than  the  neighboring  lapilli  craters,  as  its 
surface  is  free  from  the  debris  showered  over  the  island 
when  they  were  formed.  The  lava  descends  into  the  lake 
without  change  of  character,  thus  indicating  that  the  sur- 
face of  the  water,  at  the  time  of  its  extrusion,  was  lower 
than  now.  The  distinctions,  however,  between  the  char- 
acteristics of  a  subaerial  and  a  subaqueous  lava  flow  are 
not  sufficiently  well  determined  to  allow  one  to  decide  in 
all  cases  in  which  manner  an  eruption  occurred. 

The  central  portion  of  the  small  lava  flow  just  descril)ed 
is  lower  than  its  sides.  After  the  sides  and  surface  had 
cooled  and  hardened,  the  still  liquid  interior  flowed  out 
and  allowed  the  surface  crust  to  subside.  On  looking 
down  on  the  surface  of  the  lava  stream  from  th  '^djacent 
elevations,  another  interesting  fact  is  to  be  noteu.  The 
apparent  chaos  of  angular  blocks  composing  it,  is  not  in 
reality  without  some  order.    The  larger  blocks  are  heaped 


••I 


216 


VOLCANOES   OF    NOUTH    AMERICA 


•I 


,  ! 


i     I 


in  crescont-shapc'd  ridgos,  which  cross  the  stream  and  are 
convex  in  the  direction  of  flow.  Several  of  these  curved 
ridges  may  be  easily  distinguished,  wiiich  are  concentric, 
one  with  another,  and  reseuible  in  a  generjil  way  the 
curved  terminal  moraines  to  l)e  seen  in  many  formerly 
glaciated  valleys.  The  wave-like  appearance  of  the  sur- 
face of  the  lava  How  is  due  to  pulsations  in  the  stream  of 
molten  rock,  caused  by  the  clogging  of  the  current  by  the 
blocks  of  hardened  lava  floating  on  its  surface. 

The  rock  forming  the  lava  fl(nv  just  descriljed  has  been 
studied  by  Professor  J.  P.  Iddings,  and  found  to  be  essen- 
tially a  hypersthene  andesite,  although  its  microscopic 
structure  is  somewhat  indefinite.  It  is  on  the  dividing 
line  between  andesite  and  basalt,  but  apparently  the 
weight  of  evidence  places  it  in  the  former.  It  is  a  black, 
fine-grained,  couipact  rock,  breaking  with  a  conchoidal 
fracture,  and  to  the  field  geologist  has  all  the  appearance 
of  basalt,  but  is  free  from  olivine. 

This  outwelling  of  lava  came  from  near  the  base  of  the 
lapilli  crater  described  above.  It  is  the  latest  extruded 
material  on  Paoha  Island,  and  probably  the  last  igneous 
discharge  in  Mono  valley. 

Negit  Island  is  composed  of  a  crater,  and  of  a  coulee 
of  lava  which  extends  a  third  of  a  mile  southward  from 
its  base.  The  recent  origin  of  the  island  is  attested  by 
the  absence  of  lacustral  deposits,  but  a  thin  coating  of  cal- 
careous tufa  extending  twenty  feet  above  the  1883  level 
of  the  lake,  shows  that  the  coulee  is  of  somewhat  older 
date  than  the  similar  lava  streams  on  Paoha  Island.  The 
rocks  composing  Negit  Island  are  even  more  basaltic  in 
appearance  than  those  of  its  neighbor,  but  are  classed  by 
Iddings  as  hypersthene  andesite.     The  crater  is  unlike  any 


'* 


VOLCANUKS  OF  NOUTir   AMKRICA. 


PI.ATK  8. 


^V, 


"■.^f^A:v:: 


'anumCritisr  ;,  '.  ■;"■■■,.'■■  ■'.'■'■■■"''*'*:'/"''•'•■•'  ■''>■>•'' 
/  ■'■■.  '■•'•-■.■    •:  "'.ji' •;';■.',':'■■.•;  ;  ■:'  :'■.'.■■.  .:■,•,;■•  ''^.'■'.  ''.VV;. 


>.- 


I« 


•;•••  .•■\i'  •  •  ■■.  ^>.  ■■  ■,  (.-  •'.■  ■■■>■■■■■-  ^^'t  •• 


''tV.^!  '-'V  .       t^'-TSKflff^  ,''      •■  J^<  .■■'  "/J 


olMWBuH 


y-^^^S,... 


■  '   ««l-'':>-'V.>;/./'  ....    •;•,■ 

■ '  "!*:;■•■"■  ■  •    


^V/ 


::^ 


u^ 


2oi<Q'- Sit- '■;-;^\' •••■;:■■.■••:  ■■•••■■■••■••'.v'-.v 

lti*~ -,HK  •".■;■■■■.'>  ■■•.■.■..■•.■■. '. 


■::rm-K: 


:':S':- 


> 


^>i^^:i^:v,'5?p  .;;:,\;;^;  v^^l.^  Vy--,.  ,.>:v. 


MONO    CRATERS 

3  3 


^  i 


^    1 


J.  ■ 


'f    Ml 


4  mile;. 


Elevations  al)ove  Lake  Mono  srivpn  in  feet. 


'fl 


ti 


I 


-=_    ,"  •— a: 


•gy— *  i  fiw  ■  ■  iBgysiiiraMU'a;^^ 


^* 


( » 


ff 


If. 


I 


1 


VOLCANOKM   (»K   TIIK    I'NITED   8TATKM 


•-'17 


other  in  Monu  valley.  juhI  is  not  a  lii')illi  cone,  but  is  com- 
posed of  scoria,  which  was  ejected  in  large  aenii-plastic 
masses.  No  dust  or  lapilli  is  scattered  over  the  rugged 
surface  of  the  black  lava. 

The  crags  and  isolated  rocks  in  Mono  Lake  to  the  north 
of  the  two  principal  islands,  are  fragments  left  by  erosion 
of  ancient  mica  andesite  (also  a  volcanic  rock)  similar  to 
the  l)asement  rock  beneath  the  lacustral  marls  and  recent 
hipilli  dei)osits  of  Paoha  Island. 

From  the  Negit  Island  southward  to  the  end  of  the 
Mono  (;raters,  when  they  come  down  nearly  to  the  lake 
shore,  is  but  a  little  over  four  miles.  When  the  wind  is 
fair,  this  distance  is  quickly  sailed.  On  approaching  the 
shore,  we  find  it  fringed  with  a  broad  belt  of  white  frotii. 
The  alkaline  waters  are  easily  churned  into  foam,  which 
after  a  gale  is  frequently  two  or  three  feet  deep,  and  is 
blown  ashore  in  cotton-like  masses,  that  are  rolled  along 
by  the  wind,  and  even  reach  the  desert  vegetation  fring- 
ing the  desolate  area  near  the  lake  shore.  Let  us  continue 
our  excursion  by  ascending  the  Mono  craters. 

The  Mono  Craters. — The  grouping  of  these  craters  and 
the  positions  of  the  coulees  of  lava  that  have  flowed  from 
them  are  shown  on  the  map  forming  Plate  8.  They 
form  a  slightly  crescent-shaped  range  of  mountains,  ex- 
tending south  from  Mono  Lake  to  a  distance  of  about  ten 
miles.  More  than  twenty  complete  or  partially  Ijuried 
craters  can  be  recognized.  Others  are  no  doubt  concealed 
beneath  the  products  of  the  more  recent  eruptions. 

The  highest,  and,  judging  from  their  eroded  condition, 
the  oldest,  of  the  well-defined  cones  in  the  range  are  in  its 
central  part.  The  four  higher  summits  rise  in  order  from 
north  to  south,  2455,  2749,  2620,  and  2595  feet,  respec- 


I 


t    ti 


J 


! 


I 


I 


/» 


!  I, 

,r  I 

! 


j": 


i 


:! 


I  ! 


Ill 


!!'! 


,,i 


SI 


\'J 


I 


I 


218 


VOLCVXOES   OF    NORTH    AMEltlCA 


lively,  above  the  surface  of  Mono  Lake,  which,  as  previ- 
ously stated,  is  C380  feet  above  the  sea. 

The  Mono  craters  are  composed  largely  of  clastic  ma- 
terial, of  which  a  light  gray  lapilli  forms  the  greater  part. 
Tliere  are  also  several  coulees  of  lava  which  flowed  out  in 
a  molten  condition  and  consist,  in  large  part,  of  a  denh,. 
black  glass  termed  ohsidicm.  These  two  methods  of  ex- 
trusion have  produced  striking  contrasts  in  the  form  and 
color  of  various  portions  of  the  range. 

The  accumulations  of  lapilli  have  a  light  gray  tint,  and 
smooth,  even  contours.  All  of  the  cones  are  composed,  to 
a  large  extent,  of  this  material  and  are  especially  pleas- 
ing and  beautiful  to  the  eye  on  account  of  their  graceful 
carves  and  soft,  harmonious  tints.  In  marked  contrast 
with  the  lapilli  deposits  are  thick  sheets  of  black  ob- 
sidian of  recent  date,  which  have  flowed  in  various  direc- 
tions and  usually  from  nea:  the  crest  of  the  range.  The 
surfaces  of  these  overflows  are  angular  and  rugged  to  the 
last  degree.  As  shown  on  the  accompanying  map,  one  of 
these  outpourings  of  volcanic  glass  occurs  near  the  south- 
ern end  of  the  range  of  craters,  and  another  of  less  size 
near  its  northern  end. 

Owing  to  the  highly  viscous  condition  of  the  lava  of 
these  coulees  at  the  time  of  its  extrusion,  it  formed  thick 
sheets,  which  terminate  in  precipices  betv.een  200  and 
300  feet  high.  The  slow-roovinsj:  lava  congealed  and 
came  to  rest  on  slopes  so  steep  that  it  seems  almost  a 
miracle  that  they  should  have  remained  in  such  positions. 

The  contrast  presented  by  the  lapilli  deposits  and 
coulees,  which  consist  of  the  same  magma  cooled  under 
different  conditions,  is  most  striking.  The  fragments 
composing    the   former   are   open   in   texture,   vesicular, 


VOLCANOES   OF   THE   UNITED   STATES 


•JIO 


light-colored,  aiul  funii  siiiootli,  oven  slopes  with  incli- 
nations of  about  30";  the  obsidian  is  a  dense,  black  glass 
without  cavities  or  steam  l)lebs,  but  al)ounds  in  stony 
inclusions,  and  frequently  has  its  surface  dusted  over 
with  lapilli  that  fell  upon  it  while  it  was  still  somewhat 
plastic. 

The  Mono  craters  are  markedly  different  from  any 
other  volcanoes  in  the  United  States  now  known.  The 
rock  composing  them  is  a  rhyolite,  and  is  highly  acidic. 
It  presents  marked  contrasts  to  the  basic  material  com- 
posing the  great  majority  of  recent  volcanic  rocks  the 
world  over.  The  volcanic  history  of  ^Nlono  valley  will 
repay  more  careful  study  than  it  has  thus  far  received, 
for  the  reason  that  the  phenomena  there  so^  well  dis- 
played are,  in  a  great  measure,  unique. 

As  previously  stated,  the  lofty  central  cones  in  the 
Mono  craters  are  considerably  eroded  and  have  lost  their 
craters.  Their  summits  are  blunted  and  the  removal  of 
lapilli  has  exposed  crags  of  rough  lava.  The  volcanic 
energy  early  in  the  history  of  the  range,  evidently  found 
an  avenue  of  escape  where  the  central  cones  now  stand ; 
and  when  the  conduits  of  these  craters  becan"3  clogged, 
newer  craters  Avere  formed  botli  to  the  north  and  south 
along  the  same  line  or  belt  of  fracture.  In  general,  tlie 
craters  appear  fresher  and  fresher  the  more  remote  they 
are  from  the  centre  of  the  range.  A  good  illustration  is 
thus  furnished  of  the  well-known  fact  that  volcanoes  are 
frequently  located  on  fissures  and  that  when  one  conduit 
becomes  closed  others  are  opened  along  the  same  line  of 
fracture.  More  could  be  said  in  thi;r  connection  in  refer- 
ence to  the  volcanoes  of  the  Mono  region,  since  the  Mono 
craters,  although  a  unit  in  themselves  and   forming  an 


p-« 


rt 


220 


VOLCANOES    OF    NORTH    AMERICA 


;».    i 


..  i 


;     * 


isolated  and  well-defined  group,  are  in  fact  a  portion  of 
a  much  more  extended  series  of  recent  eruptions,  which 
follow  the  general  course  of  the  great  b(;lt  of  branching 
faults  which  determines  the  eastern  face  of  the  Sierra 
Nevada.  Tlie  craters  on  the  island  in  Mono  Lake  are  on 
this  belt  of  disturbance.  Northwest  of  the  lake  there  are 
other  volcanoes.  South  of  the  Mcjno  crater  the  same  belt 
of  recent  cones  is  continued  and  is  marked  by  recent 
craters  of  both  acidic  and  basic  lava,  for  at  least  a  score 
of  miles. 

There  are  some  exceptions  to  the  statement  that  the 
most  recent  eruptions  occurred  at  the  ends  of  the  Mono 
craters,  since  two  or  three  of  the  smaller  craters  irdr  the 
centre  of  the  range  and  high  up  on  the  flanks  of  the  large 
central  cones,  are  fresh  in  appearance  and  possibly  as 
recent  as  the  vents  at  the  extremities  of  the  series. 

The  craters  which  still  preserve  their  shapes  and  show 
but  slight  evidence  of  having  been  modified  by  erosion 
may,  for  convenience  of  description,  be  divided  into  two 
groups,  although  in  reality  there  is  no  true  dividing  line 
between  them.  In  the  case  of  the  craters  forming  the 
first  of  these  groups,  the  lapilli  fell  on  all  sides  of  the 
place  of  extrusion  i;nd  built  up  symmetrical  rings,  enclos- 
ing conical  basins.  Some  of  these  are  depressed  bowls 
with  scarcely  a  vestige  of  a  raised  rim  about  them ;  while 
others  are  well-defined  cones  rising  steeply  from  the  sur- 
rounding surface,  and  have  deep  conical  depressions  in 
their  summits.  Tlie  craters  of  the  second  group  are 
similar  to  those  just  mentioned,  except  that  they  gave 
egress  to  molten  lava. 

The  craters  that  were  points  of  eruption  for  both  lapilli 
and  lava  may  again  be  divided  into  two  groups:  (1)  Those 


VOLCANOES    OF   THP]    UNITED   STATES 


221 


in  which  the  lava  did  not  escape  from  the  IjowLs  formed  by 
the  violent  extrusion  of  fragmental  material,  and  (2)  those 
from  which  the  lava  overflowed  and  formed  more  or  less 
extensive  coulees.  As  may  be  seen  at  a  glance,  these 
variations  depend  simply  on  differences  in  the  intensity 
of  the  volcanic  activity.  The  first  eruption  in  each  in- 
stance was  a  violent  ejection  of  connninuted  and  usually 
scoriaceous,  but  at  times  compact  and  glassy  rhyolite. 
In  the  craters  formed  entirely  of  lapilli,  the  eruptions 
ended  at  this  point.  In  other  instances,  an  escape  of 
viscid  lava  took  place  through  the  same  conduit  from 
which  the  lapilli  came.  In  some  cases  when  an  upwell- 
ing  of  lava  occurred,  it  barely  entered  the  bottom  of  the 
bowl  of  lapilli  before  becoming  congealed.  The  eruption 
then  ceased,  so  far  as  that  individual  vent  was  concerned. 
At  other  times,  the  thick,  viscid  lava  was  forced  up  in  the 
centre  of  the  crater  until  it  stood  higlier  than  the  encir- 
cling rim  of  lapilli  but  did  not  expand  laterally.  In  in- 
stances of  this  nature  there  is  a  deep,  moat-like  depression 
between  the  rough  and  angular  protrusion  of  lava  and  the 
smooth  inner  slope  of  the  encircling  crater,  in  which  one 
may  walk  entirely  around  the  ce  .tral  tower-like  mass. 
The  type  of  this  variety  of  eruption  is  furnished  by  the 
crater  shown  in  the  following  illustration,  which  stands 
near  the  shore  of  Mono  Lake  and  has  been  named  Panum 
crater. 

Where  the  upwelling  of  lava  was  larger  in  amount,  it 
broke  through  the  encircling  rim  of  lapilli  and  flowed 
away  as  a  stream,  or  coulee,  of  lava,  which,  on  account 
of  its  viscous  nature,  —  characteristic  of  all  the  lava 
flows  from  the  Mono  crater,  —  ended  in  a  steep  border 
composed  of  angular  blocks.    The  surfaces  of  the  streams, 


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VOLCANOES   OF    NORTH    AMERICA 


in  all  cases,  also,  are  of  this  same  character ;  their  broken 
and  angular  condition  being  due  to  the  rapid  cooling  uf 
the  lava  at  the  surface,  while  the  interior  was  still  i)lastic 
and  moving.  Tlie  surfaces  of  the  streams  are  sometimes 
highly  vesicular,  and  so  filled  witli  steam  bubbles  that  the 
rock  is  a  true  pumice  ;  at  other  times,  especially  in  the 
case  of  the  larger  streams,  the  blocks  are  of  dense  black 
obsidian.  To  walk  on  the  chaos  of  angular  fragments,  in 
the  latter  instance,  is  like  crossing  a  field  covered  deeply 
with  huge  blocks  of  broken  glass. 


Fio.  8.    Panum  Crater :  Lake  Mono  and  Paoha  Island  in  the  distance.     (From  a 

photograph.) 

Some  of  the  variations  presented  by  the  Mono  crater, 
due  to  differences  in  the  relative  amounts  of  lapilli,  and  of 
lava  extruded,  are  indicated  in  the  following  series  of 
cross-sections  of  a  few  of  the  craters.  These  are  sketch 
sections  and  are  not  drawn  to  a  uniform  scale. 

In  the  diagram,  a  is  a  depression  in  a  field  of  lapilli, 
and  has  a  level  floor  of  the  same  material ;  6  is  a  lapilli 
crater,  also  floored  with  material  of  the  same  character 
as  that  forming  the  rim  ;  c  is  a  crater  similar  to  h,  except 
that  a  few  crags  of  scoriaceous  rhyolite  in  its  bottom  mark 


mf 


VOLCANOES  OF   THE   UNITED   STATES 


'223 


the  position  of  the  summit  of  a  phig  of  hiirdened  lava,  that 
exists  beneath  ;  in  the  crater  marked  d,  the  hiva  has  risen 
so  as  to  be  higher  tlian  the  wall  of  lapilli  encircling  it; 
this  is  intended  to  show  the  condition  existing  in  Pannni 
crater,  illustrated  also  in  Plate  8.  A  oontinnation  of  the 
sei'ies  might  be  made  by  adding  cross-sections  of  craters 
in  which  the  lava  has  broken  through  a  rim  of  lapilli  and 
advanced  on  the  adjacent  surface.  Figu?'e  e  illustrates 
still  another  variety  of  crater  which  is  represented  by  at 
least  one  example,  the  steep-sided  depression  in  this  in- 
stance is  due  to  the  subsidence  or  retreat  of  the  lava  which 


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Fi<i.  9.    Cross-sections  of  some  of  the  Mono  craters. 


once  rose  within  a  crater  of  lapilli.  Figure  /  is  a  small 
cone  composed  of  scoria  which  was  thrown  out  in  a  plastic 
condition  and  piled  up  around  the  vent.  The  last  ex- 
ample occurs  at  ihe  edge  of  a  coulee,  at  the  north  end  of 
the  range,  and  is  about  seventy-five  feet  deep. 

The  craters  in  which  volcanic  action  was  most  ener- 
getic gave  origin  to  coulees  of  lava,  as  already  stated. 
When  this  occurred,  the  craters  of  loose  incoherent  lapilli 
were  breached  and  sometimes  entirely  destroyed.  One  of 
the  smaller  lava  flows  near  the  north  end  of  the  range 
may  be  traced  directly  to  the  crater  from  which  it  origi- 
nated, of  which  only  a  small  portion  now  remains.  In 
the  case  of  the  larger  overflows,  designated  on  the  accom- 


■■■■■mtmmimmm 


224 


VOLCANOES   OF   NORTH   AMERICA 


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panying  map  as  the  Northern  and  Southern  coulees,  no 
vestiges  of  the  crater  from  which  the  hiva  came  can  now  be 
seen.  The  obsidian  composing  those  streams  was  extruded 
in  a  thick,  viscid  condition,  and  iiowed  slowly  down  the 
steep  mountain  side.  The  Northern  coulee  congealed  be- 
fore reaching  level  ground,  but  the  Southern  coulee,  after 
descending  the  mountain  slope,  advanced  nearly  a  mile  on 
the  plain  and  finally  came  to  rest  with  a  steep  and  exceed- 
ingly rugged  outward-forcing  escarpment. 

As  shown  on  the  map,  the  Southern  coulee  invaded  a 
region  formerly  occupied  by  a  glacier,  and  obliterated  the 
npptu-  portion  of  a  deep  stream-channel  made  by  the  water 
that  flowed  from  the  melting  ice.  The  smooth,  evenly 
curved  ridges  sweeping  out  from  the  vicinity  of  June  Lake, 
shown  in  the  southwest  corner  of  the  map,  are  moraines 
left  by  a  large  glacier.  The  lava  stream  is  more  recent 
than  the  recession  of  the  end  of  the  glacier,  the  bed  of 
which  it  now  occupies,  and  of  late  Pleistocene  age. 

Additional  evidence  that  some  of  the  Mono  craters 
were  in  a  state  of  violent  eruption  after  the  existence 
of  the  glacier  of  the  Sierra  Nevada,  is  furnished  by 
deposits  of  fine,  nearly  white  rhyolitic  dust,  which  cover 
several  of  the  moraines  in  the  southern  portion  of  Mono 
valley.  Similar  dust  deposits  are  strewn  for  hundreds  of 
square  miles  over  the  adjacent  region.  These  will  be 
described,  together  with  other  similar  accumulations,  in 
a  future  chapter.  As  is  represented  also  on  the  accom- 
panying map,  there  is  a  small  crater  half  a  mile  north  of 
June  Lake,  which  was  formed  previous  to  the  advance  of 
the  glacier  referred  to  above,  and  was  partially  removed 
by  the  ice  which  flowed  over  it. 

Other  features  of  Mono  valley  which  are  of  interest  to 


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VOLCANOES   OF  TIIK    UNITED   STATES 


225 


the  student  of  volcanic  phenonienii  might  he  descrihed, 
hut  as  one  of  the  ohjects  of  this  hook  is  to  k;ad  the  reader 
to  consult  original  monographs,  1  must  refer  those  wIkj 
desire  to  pursue  the  suhject  further,  to  the  report  from 
"which  the  data  given  ahove  has  mtjstly  heen  taken.' 

Mt.  Shasta,  California.  —  In  travelling  northward 
through  the  hroad  Sacramento  valley,  one  has  hefore 
him  a  lofty,  snow-crowned,  conical  mountain,  which 
stands  alone  and  is  the  dominant  feature  in  the  land- 
scape. This  attractive  ohject  is  Mt.  Shasta,  a  typical 
volcanic  mountain.  The  main  summit  has  lost  the 
freshness  of  youth  and  is  seamed  with  radiating  ra- 
vines and  gulches,  which  have  resulted  from  the  work 
of  streams  and  glaciers.  Some  of  these  features  may  be 
recognized  in  the  photograph  forming  Plate  9. 

Mt.  Shasta  has  an  elevation  of  14,350  feet,  and  towers 
a  mile  in  vertical  height  above  its  nearest  neighbor.  The 
summit  is  more  than  4000  feet  above  the  timber  line,  and 
is  occupied  by  small  glaciers.^  The  upper  3000  feet  of 
the  mountain's  side,  where  cliffs  are  most  abundant,  has 
an  average  slope  of  nearly  35°  ;  farther  down,  the  in- 
clination becomes  more  gentle.  The  base  of  the  moun- 
tain is  seventeen  miles  in  diameter,  and  its  altitude  above 
its  base,  or  its  visual  height,  is  over  two  miles.  Its 
volume  is  in  the  neighborhood  of  eighty-four  cubic 
miles. 

On  the  west  side  of  Mt.  Shasta,  2000  feet  lower  than 
the  main  summit,  is  a  well-developed  cone  with  a  crater 
in  its  top,  known  as  Shastina.    On  the  lower  slopes  of  the 

^  I.  C.  Russell,  "Quaternary  History  of  Mono  Valley,  California,"  in  8th 
Annual  Report  of  the  U.  S.  Geological  Survey',  1880-87. 

^  These  glaciers  are  described  in  "  Glaciers  of  Xorth  America,"  by  I.  C. 
Russell,  pp.  55-62.    Ginn  &  Co.,  Boston,  18!)7. 


i 


226 


VOLCANOES   OF   NOUTIF    AMKUTCA 


mountain,  and  in  the  region  surrounding  it,  tliero  are  a 
number  of  smaller  craters,  some  of  them  built  of  cinders, 
and  others  of  lava.  The  mountain  is  composed  of  lava 
flows  with  a  minor  quantity  of  scoria. 

On  the  flanks  of  Shasta  there  are  well-defined  lava 
streams  whicrh  still  retain  tin;  rough,  angular  surfaces 
given  to  them  when  the  viscid  magmas  flow(id  out  and 
cooled  in  thick  sheets  which  terminate  on  stee})  slopes 
with  precipitous  terrace-like  borders.  One  of  these 
coulees  on  the  northwestern  side  of  the  mountain,  and 
at  an  altitude  of  from  5000  to  GOOO  feet,  forms  what 
has  been  named  Lava  Park.  Judging  from  the  fresh- 
ness of  the  rock,  this  is  the  youngest  coulee  on  the 
mountain.  The  slope  over  which  the  lava  flowed  was 
comparatively  geuth^  so  that  it  spread  broadly,  and 
formed  a  sheet  nearly  as  wide  as  hjug.  The  park  is  an 
exceedingly  rough  lava  field,  about  two  sfjuare  miles  in 
area,  on  which  so  little  ^oil  has  formed  that  forest  trees 
have  not  taken  root.  The  lava  at  the  time  of  its  extru- 
sion was  viscous,  and  on  coming  to  rest  formed  a  steep 
escarpment  about  its  lower  margin. 

Another  conspicuous  coulee  similar  to  the  one  forming 
Lava  Park  esca})ed  from  the  western  side  of  the  moun- 
tain at  an  elevation  of  5000  feet,  and  followed  north- 
westward  in  a  rather  narrow  stream  for  several  miles. 

The  longest  and  most  copious  of  the  more  recent  lava 
streams  that  flowed  from  Mt.  Shasta  issued  from  its 
southern  side  at  an  elevation  of  about  5500  feet.  This 
stream  divided  into  two  branches,  one  of  which  is  twelve 
miles  long ;  the  other  entered  the  cauvon  of  Sacramento 
River  and  reached  a  distance  of  fifty  miles  from  its  source 
before  cooling  checked  its  advance.    That  the  lava  stream 


VOLCANOKS   OF   THE    LNITKD   STATES 


•J27 


wliioli  (]is|)l;icc(l  Sucraiucnto  River  is  of  soincwhiit  Jinciciit 
datii,  as  inuasurod  in  years,  is  shown  hy  tlie  amount  of  ero- 
sion it  has  sulYered.  Not  only  has  tlie  river  eut  throu>;h 
tlic  liardeiied  lava,  partially  fdling  its  ancient  chainiel, 
leaving  portions  of  the  lava  rock  as  a  terrace  on  the 
border  of  the  canyon,  but  has  excavated  a  narrow  gorge 
more  than  a  hundred  feet  deep  into  the  rocks  Ijcueath. 

The  lava  streams  mentioned  above  show  no  (evidence 
of  having  been  glaciated,  but  retain  their  original  rough- 
ness of  surface.  They  are  considered  as  being  of  more 
recent  date  than  the  time  when  the  glaciers  llcjwinu'  from 
the  summit  of  the  peak  reached  the  plain  below.  That 
is,  the  most  recent  lavas  were  poured  out  subscijuently 
to  the  Glacial  epoch. 

As  shown  })y  J.  S.  Diller,  the  post-glacial  coulees,  how- 
ever, form  only  a  thin  cover  on  the  sloix's  of  Mt.  Shasta. 
The  great  mass  of  the  lava  composing  the  mountain  was 
extruded  previous  to  the  last  great  climatic  change  which 
enabled  the  glaciers  starting  at  its  summit  to  How  to  the 
plain  below.  Although  the  great  body  of  the  mountain 
is  made  up  of  coulees  of  lava,  it  contains  a  large  propor- 
tion of  fragmental  material,  and  must  be  considered  as 
a  mixed  or  compound  cone. 

As  already  stated,  Mt.  Shasta  is  a  doul)le  cone,  —  Mt. 
Shasta  proi)er,  and  Shastiua.  These  two  sunuuits  are 
so  closely  united  that  tlu!y  make  but  one  cone  Ijelow  an 
altitude  of  10,000  feet.  Besides  the  two  jn-incipal  vents 
there  are  remnants  of  more  than  a  score  of  subsidiary 
ones  which  contributed  to  the  upbuilding  of  the  moun- 
tain. Many  other  secondary  points  of  eruption  are  no 
doubt  conc(,'aled  beneath  the  u;reat  coulees  now  formins 
the  outer  sheathing  of  the  great  cone. 


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VOIX'ANOKS   OK   NOllTII    AMKUICA 


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Tilt'  LJirt'ful  studies  of  Mi.  Sli.ista  contliictcd  \>y  Dillur 
liavu  sliuwii  tliat  it  is  c()in[)<)scMl  of  in.iiiy  variclii's  of 
volcanic  rock.  Its  chief  const  it  lU'iits,  however,  arc  amlL'- 
sitc,  rhyolitc,  and  basalt.  The  iiKtst  ahuiidant  rock  is 
hypersthene  aiidesite  —  a  lava  containing  little  or  nu 
hornhlcnde.  hut  much  h}[)ersthene.  It  ranges  in  color 
from  light  and  dark  gray,  often  reddish,  to  l)lack.  lia- 
salt  occurs  only  on  the  lower  slopes  of  the  mountain,  but 
forms  nearly  all  of  the  numerous  cinder  cones  on  the 
adjacent  plain. 

One  of  the  interesting  features  of  the  lower  slope  of 
the  mountain  is  Pluto's  cave,  formed  by  the  flowing  out 
of  the  central  portion  of  a  lava  stream  after  its  surface 
had  cooled  and  hardened.  This  cave  where  best  devel- 
oped is  from  sixty  to  eighty  feet  in  height,  from  twenty 
to  seventy  broad,  and  has  been  followed  f(jr  nearly  a  mile 
without  finding  its  extremity.  The  floor  of  the  cavern  is 
nearly  flat  and  covered  with  debris  that  has  fallen  from 
the  sides  and  roof.  The  roof  above  it  is  from  ten  to 
seventy-five  feet  thick,  and  the  lava  of  which  it  is  com- 
posed is  full  of  cavities  formed  by  the  expansion  of  steam 
while  the  magma  was  still  plastic. 

Many  other  interesting  and  instructive  facts  concerning 
Mt.  Shasta  may  be  found  in  the  graphic  and  most  attrac- 
tive monograph  from  which  this  account  has  been  largely 
compiled.' 

Cinder  Cone,  near  Lassen's  Peak,  California.  — The  Las- 
sen's peak  district  is  situated  in  northern  California  be- 
tween   the    Sacramento   valley   and   the   broad   area   of 

1  J.  S.  Diller,  "  Mount  Shasta,  a  Typical  Volcano,"  National  Geographic 
Monographs  (published  under  the  auspices  of  the  National  Geographic  So- 
ciety, by  the  .\nierican  Book  Co.),  Vol.  I,  1895,  pp.  237-2(58. 


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VOLCANOES    OF    THE    UNITED   STATES 


229 


interior  drainage  to  the  east,  known  as  the  Great  Basin. 
The  volcanic  peak  from  wliich  the  district  derives  its 
name  rises  10,437  feet  aljove  the  sea,  and  is  considered 
as  marking  tlie  soiitliern  terminus  of  the  Cascade 
Mountains. 

The  Lassen's  peak  district  is  crossed  from  northwest  to 
southeast  l)y  a  belt  of  volcanic  cones,  abort  lifty  miles 
long  and  twenty-five  miles  wide.  The  great  peaks  which 
form  the  dominant  features  of  this  ridge  are  Butte  moun- 
tain, Lass^ij's  peak,  Crater  peak,  and  Burney  butte.  Be- 
sides these  there  are  many  smaller  conical  hills,  which  are 
also  of  volcanic  oriuin. 

By  far  the  most  abundant  rocks  in  the  Lassen's  peak 
district  are  those  that  have  cooled  from  a  fused  condition 
and  are  both  intrusive  and  extrusive.  They  exliil)it  great 
variety,  oi  account  of  differences  in  structure  and  in  min- 
eralogical  and  chemical  composition,  and  range  from 
basalts  having  as  low  as  forty-nine  per  cent  of  silica, 
through  andesites  and  dacites  to  rhyolites,  some  of  which 
contain  over  seventy-four  per  cent  of  silica. 

The  latest  volcanic  eruption  in  the  district  briefly 
described  above,  occurred  at  what  is  known  as  the  Cinder 
cone,  ten  miles  northeast  of  Lassen's  peak.  A  general 
view  of  this  locality,  taken  from  a  neighboring  summit  to 
the  northward,  is  shown  on  Plate  10,  Fig.  A.  A  map  of 
the  same  locality  is  presented  on  Plate  11.  As  shown  in 
these  illustrations,  the  most  striking  topographic  feature 
of  the  region  is  a  conspicuous  and  very  characteristic  cin- 
der cone,  from  the  base  of  which  a  rugged  and  exceedimrlv 
fresh-looking  lava  coulee  has  flowed  and  spread  out  over 
the  adjacent  plain. 

On  approacliing  the  Cinder  cone  one  finds  the  surface, 


I     ! 


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230 


VOLCANOKS    (JF    NoltTll    A.MKUICA 


where  not  occupied  by  lava,  to  l)e  covered  with  soft,  dull, 
black,  volcanic  sand.  At  iirst  this  deposit  is  only  a  few 
inches  thick,  l)ut  near  the  base  of  tlie  cone  it  becomes 
Cijarser  and  deei)er.  What  thickness  it  attains  in  the 
immediate  vicinity  of  the  C(jne  is  unknown,  but  one- 
fourth  of  a  mile  away  in  all  directions,  it  is  about  seven 
feet  d  p  and  decreases  in  alnuidance  gradually  so  as  to 
disappear  at  a  distance  of  eight  miles.  Encircling  the 
Cinder  cone  at  its  base,  is  a  collection  of  volcanic  bombs, 
ranti;inti;  in  size  from  a  few  inches  to  eight  feet  in  diam- 
eter.  They  are  nuich  fissured,  and  many  of  tiiem  have 
fallen  to  pieces,  showing  an  interior  of  compact  lava,  while 
the  surface  is  somewhat  scoriaceous  and  ropy. 

On  clind)ing  the  Cinder  cone,  one  finds  it  to  be  com- 
posed of  loose  scoria  and  Lipilli.  In  I'oi-m  and  composi- 
tion and  in  fact  in  all  its  essential  features,  it  reseml)les 
the  summit  portion  of  Vesuvius.  The  cone  is  regular  in 
form,  with  a  surprisingly  smooth,  dark  surface,  and  shows 
no  traces  of  waterways  or  other  evidences  of  erosion.  It 
rises  to  an  elevation  of  640  feet  above  the  lowest  point  at 
its  base,  which  is  0007  feet  aljove  the  sea.  Its  diameter 
at  the  base  is  2000  feet  and  750  feet  across  the  truncated 
summit.  The  slopes  are  as  steep  as  it  is  possible  for  the 
material  of  which  it  is  composed  to  lie,  and  in  places  is 
marked  by  slides.  The  angle  of  slope  varies  from  30°  to 
37°.  The  dull,  sombre  aspect  of  the  smooth,  barren  slope 
is  greatly  relieved  ))y  carmine  and  orange  colored  lapilli 
on  its  southeastern  side. 

At  the  summit  of  the  cone,  as  shown  in  the  following 
illustration,  there  is  a  well-developed  crater  with  a  double 
rim.  The  central  funnel-shaped  depression  is  2-40  feet 
deep. 


VOLCANOES   OF   NOKTH   AMKHICA. 


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VOLCANOES   OF    THE    UNITED   STATES 


231 


Tlie  lava  field  about  the  Cinder  cone  has  an  area  of 
about  two  and  one-third  square  miles,  and  at  its  borders 
terminates  in  precipitous  scarps,  m  places  over  100  feet 
high.  Within  the  lava  lield  and  about  its  borders  in 
certain  places,  there  are  deposits  of  soft  white  diatoma- 
ceous  earth.  This  is  a  lacustral  deposit,  composed  largely 
of  the  siliceous  cases  of  unicellular  plants,  known  as 
diatoms,  and  is  at  least  ten  feet  thick.  The  ))earing  of 
this  deposit  on  the  history  of  the  volcano  will  be  seen  in 
the  followii.g  summary,  published  Ijy  Diller,   in  the  geo- 


Fij;.  10.  Sketcli  of  the  crater  of  the  cinder  cone  near  Lassen's  peak,  (Jalifornia, 
sliowin.u  the  i)eciiliar  feature  of  two  rings,  of  wliicli  the  inner  one  encircles  u 
fnnnel  2-10  feet  deep.     (.1.  S.  Diller.) 

logical  folio  where  the  facts  just  enumerated  are  descriljed 
and  discu.ssed.' 

"  The  facts  just  mentioned  show  that  there  were  at 
least  two  periods  of  eruption  from  the  Cinder  cone,  and 
that  they  were  separated  by  a  time  interval  sufficiently 
long  to  allow  ten  feet  of  infusorial  (diatomaceous)  earth 
to  accumulate  on  the  ancient  bottom  of  Lake  Bid  well. 
The  first  period  was  characterized  by  a  violent  explosive 
eruption,  which  formed  the  Cinder  cone  and  ash  lield ; 
the  second,  by  a  quiet  effusion  of  a  large  mass  of  lava. 

1  J.  S.  Diller,  "  Geological  Atlas  of  the  United  States  "  (published  by  the 
V.  S.  Geological  Survey),  Lassen  peak  folio.  18!)").  This  folio  contains 
excellent  topographical  and  geological  maps  of  the  region  about  Lassen 
peak,  and  a  condensed  account  of  the  geology  of  the  region. 


232 


VOLCANOKS   OF   NOUTH   A MEUICA 


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'•The  first  eruption  bugan  witli  au  xplosion  and  the 
ejection  of  a  great  deal  ot"  light  scoriaceons,  almost  punii- 
ceous  material,  blown  chiefly  by  escaping  steam  from  the 
upi)er  portion  of  the  molten  lava  (magma)  in  the  throat 
of  the  volcano.  Succeeding  the  explosion  and  the  erup- 
tion of  the  pumiciform  material,  and  continuous  with  it, 
came  the  volcanic  sand,  lapilli,  scoria),  and  bombs.  They 
fell  about  the  hole  from  which  they  were  blown,  and  by 
their  accumulation  built  up  the  Cinder  cone,  which  is 
C(jniposed  almost  wholly  of  fragmental  material. 

"  After  the  greater  portion  of  the  fragmental  material 
had  been  ejected  the  magma  rose  in  the  Cinder  cone,  and 
l)ursting  it  asunder,  flowed  over  the  southeastern  portion 
of  its  base.  This  effusion  was  accompanied  and  succeeded 
by  a  shower  of  sand,  which  may  have  given  rise  to  the 
inner  rim  of  the  crater,  and  formed  a  thin  coating  over 
the  lava  already  effused.  Whether  or  not  the  effusion  of 
the  oldest  lava  and  the  succeeding  shower  of  ashes  belong 
to  the  closing  stages  of  the  first  eruption  is  not  easily  de- 
termined, but  it  is  certain  that  both  preceded  that  long 
interval  of  quiet  dtn-ing  which  the  old  lake  beds  were  de- 
posited. This  season  of  volcanic  rest  was  probably  at 
least  a  century  long,  for  to  accumulate  ten  feet  of  infu- 
sorial earth  would  ivquire  considerable  time. 

'' The  new  flow  of  lava,  .  .  .  occurred  at  the  close  of 
tlie  lake-bed  interval.  The  remarkable  characteristic  of 
this  eruption  as  compared  with  the  former  was  the  entire 
absence  of  any  explosion  from  the  crater  in  connection 
with  the  effusion  of  so  large  an  amount  of  very  viscous 
magma,  since  the  same  vent  at  an  earlier  period  had  been 
the  scene  of  a  violent  ejection. 

"  Everywhere  i!.\  the  lava  field  one  is  impressed  with 


!\V 


VOLCANOKS   OF   TIIK    UNITED   STATES 


1233 


!\^ 


the  idea  that  the  lava  of  tliis  Ihial  eruption  moved  slowly 
and  with  great  diffieulty,  repeatedly  breaking  its  crust 
and  pushing  along  as  a  great  stone  pile,  presenting  an 
abrupt  terrace-like  front  on  all  sides.  It  is  a  typical  ex- 
ample of  a  lava  field  formed  by  the  effusion  of  a  viscous 
lava  on  gentle  slopes.  Had  it  been  highly  liquid,  like 
many  of  the  other  basalts  in  the  same  great  volcanic  field, 
it  would  have  found  egress  at  the  outlet  of  Lake  Bidwell, 
and  stretched  d(jwn  the  little  valley  for  miles  to  the 
northwest. 

"  The  whole  aspect  of  the  Cinder  cone  and  lava  field  is 
so  new  that  one  at  first  feels  confident  of  finding  historic 
evidence  of  its  eruption.  .  .  .  Yet  the  evidence  clearly 
demonstrates  that  the  earliest  eruption  occurred  before 
the  beginning  of  the  present  century. 

"  Its  age  is  shown  by  the  relation  of  the  old  and  new 
forest  trees  to  the  volcanic  sand  of  the  first  eruption. 
The  living  trees  grew  upon  the  top  of  the  sand,  but  the 
dead  ones  in  the  foreground  were  standing  at  the  time  of 
the  eruption,  and  instead  of  growing  upon  the  sand,  grew 
from  the  soil  which  now  lives  beneath  it." 

The  evidence  furnished  by  the  partially  buried  trees, 
etc.,  as  stated  by  Diller,  shows  that  the  first  eruption  oc- 
curred some  two  hundred  years  and  the  second  more  than 
fifty  years  ago. 


i 


The  Great  Volcanic  Mountains  of  Oregon  and 

Washington 

Distant  views  of  the  Cascade  Mountains  show  that  they 
are  dominated  hy  a  series  of  giant  peaks,  some  of  which, 
as  Mt.  St.  Helen's  and  Mt.  liiinier,  arc  detached  from 


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VOLCANOICS    Ol'"    NUltTII    AMKIIICA 


the  main  mass,  while  others  an;  intimately  associated 
with  the  u[tlil't(Ml  lava  sheets  which  eomp(jse  a  large 
part,    hut   more   especially  of    the   southern   half,  of   the 


range. 


The  greater  volcanic  cones  which  form  such  a  pnj- 
riouncetl  and  attracti\e  feature  of  the  Cascade  region 
have  never  been  carefully  studied,  and  only  a  general  ac- 
count of  their  more  salient  features  can  he  given  at  this 
time.  The  peaks,  referred  to  in  the  order  of  their  occur- 
rence fi'om  south  to  north,  arc;  as  f(jllows;  the  ligure.s 
accompanying  the  names  of  the  jteaks  show  their  height 
above  the  sea  in  feet.  They  are:  Mt.  Pitt,  1)700;  Mt. 
Mazana,  8223  ;  Mt.  Uiuon,  78S1  ;  Mt.  Scott,  712:] ;  Three 
Sisters,  Mt.  Jefferson,  10,200,  and  Mt.  Hood  11.22-3, 
in  Oi-egon ;  Mt.  Adams,  1)070;  Mt.  St.  Helen's,  U7oO ; 
Mt.  Rainier,  14,525,  and  Mt.  Baker,  10,877,  in  Wash- 
ington. 

The  conclusion  that  these  peak.s  are  (d"  volcanic  origin 
rests,  in  some  instances,  on  their  general  appearance,  and 
their  occnrrence  in  a  volcanic  region,  rather  than  on  defi- 
nite reports  by  skilled  observers.  The  only  ones,  how- 
ever, in  reference  to  which  doubt  may  possibly  be  enter- 
tained respecting  tlieir  volcanic  origin,  are  two  or  three  of 
the  more  southerly  ones  in  Oregon. 

None  of  the  mountains  named  are  examples  of  espe- 
cially fresh  volcanic  piles,  although  nearly  all  of  them 
are  known  to  have  craters  at  their  summits,  or  on  their 
flanks.  Like  Mt.  Shasta,  they  are  for  the  most  part  the 
result  of  Tertiary  eruptions,  and  have  been  modified  by 
erosion  to  approximately  the  same  extent  in  all  cases. 
Superficially  considered,  —  careful  comparison  being  im- 
possible at  pi'esent.  on  account  of  the  lack  of  observations. 


J 


VOLCAN(.)KS   OF    TIIK    INITKI)   STATES 


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—  it  would  seem  that  tlic  liistory  of  Mt.  Shasta  lias  Ix-cn 
rc'[)eate(l,  [irobahly  with  many  minor  variations  in  each 
instance,  at  a  numl)er  of  localities  along  tlie  Cascade 
range,  and  in   its  vicinity. 

Crater  Lake,  Oregon. —  One  of  the  most  remaikaUle  of 
the  extinct  volcanoes  of  North  America,  known  as  Mt. 
^lazama,  is  situated  in  the  Ca.scade  Mountains.  Oregon, 
tiiirty  miles  north  of  Klamath  Laive,  and  is  occu^jied  by 
Crater  lake.  The  mountain  in  wiiicli  this  lake  is  situated 
is  thouglit  to  have  ))een  truncated  hy  the  mehing  and 
.subsidence  of  its  sununit.  which  left  a  rudely  circuhir 
cavity  fi-oni  live  to  six  mik's  in  diameter.  The  lake 
is  02oD  feet  abcne  the  sea.  is  11)75  feet  deep  and  sur- 
rounded by  nearly  vertical  walls  ranging  from  t)()0  to 
2200  feet  high.  The  vast  caldera  is,  then,  al)out  4000 
feet  deep.  The  fact  that  the  mountain  has  been  truncated 
is  shown  especially  by  the  character  of  the  slo[>es  that 
remain.  These  are  scarred  In  i-adiating  valleys  of  the 
same  character  as  those  on  neighboring  nuMmtains  which 
still  preserve  their  ccmical  forms,  but  open  abruptly  into 
the  central  caldera.  The  streams  that  ilowed  down  these 
iror^es,  and  to  which  their  excavation  is  mainly  due,  have 
been  beheaded  by  the  falling  in  of  the  crater  walls.  The 
outer  slopes  of  the  truncated  mountain  also  bear  evi- 
dence of  glaciation.  showing  that  before  the  great  catas- 
trophe that  removed  its  summit,  it  was  ice-cnnvned  and 
orave  oriuin  to  radiating  alpine  glaciers  of  the  same  nature 
as  those  now  to  be  seen  on  Mt.  Shasta  and  Mt.  Uainier, 
but  descending  to  a  lower  level.  Ai)parently  the  mountain 
has  lost  its  summit  since  the  Glacial  epoch. 

An  account  of  Crater  Lake,  accompanied  by  references 
to  the  writings  of  C.  Iv  Button,  l)y  whom  it  was  made 


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VOLCANOES   OF   NORTH   AMERICA 


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kiKJWii  to  gt'ulugi.sts  and  guograpliurs,  is  contiiincMl  in  a 
companion  of  tiio  volunio  before  you.' 

Mt.  Pitt. —  In  soutliern  Oregon  and  about  .sixty  miles 
north  of  Mt.  SJKusta  rises  a  beautifully  regular,  volcanic 
(Mmo  known  as  Mt.  Pitt.  Although  of  secondary  rank 
when  com[)are(l  with  several  more  lofty  summits  in  the 
Cascade  region,  yet  its  summit  and  sides  are  snow  cov- 
ered during  the  greater  part  of  the  year.  As  stated  by 
Knunons,-  there  is  a  remnant  of  a  crater  at  the  snnnuit,  the 
walls  of  which  are  broken  down,  especially  on  the  north- 
east side.  The  lavas  that  have  been  dischai'ged  from  the 
crater,  or  from  secondary  openings  on  its  sides,  resemble, 
in  general,  those  poured  out  at  Mt.  Shasta,  but  present 
certain  peculiar  features  that  promise  interesting  re- 
sults when  studied  in  the  light  of  modern  petrographic 
methods. 

Three  Sisters  and  Mt.  Jefferson. —  To  the  north  of  Mt. 
Pitt,  —  as  stated  in  the  instructive  paper  by  Emmons,  cited 
above,  —  and  in  the  main  line  of  the  Cascade  Mountains, 
the  group  of  volcanic  peaks  termed  the  Three  Sisters, 
and  a  neighboring  cone,  Mt.  Jefferson,  mark  the  sites  of 
still  other  ancient  volcanic  lights.  Little  accurate  infor- 
mation is  available  concerning  these  attractive  mountains, 
except   that   they  are  of  volcanic  origin,  although  now 


1  I.  C.  Russell,  "  Lakes  of  North  America,"  Ginn  &  Co.,  Boston,  1895, 
pp.  1*0,  '21,  and  map. 

A  map  of  Crater  Lake  with  descriptive  text  and  illustrations  has  been 
published  by  the  U.  S.  fJeolo<;ical  Snrvej-,  with  the  title  "  Crater  Lake  Special 
Map."  A  highly  instructive  paper  on  Crater  I^akes,  by  J.  S.  Diller,  may  be 
found  in  "The  American  Journal  of  Science"  for  March,  18f>7;  and  in  a 
more  popular  form  in  the  "  National  Geographic  Magazine  "  for  February, 
1897. 

2  S.  F.  Emmons,  "  The  Volcanoes  of  the  United  States  Pacific  Coast," 
in  American  Geographical  Society,  Bulletin  No.  4,  1870-77,  p.  40. 


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VOLCANOES   OF   THE    UNITED   STATES 


237 


cold  and  silent,  and  much  modified  by  erosion.  They 
form  most  beautiful  features  in  the  ma^milicent  scencrv 
of  Oregon.  Their  tapering  summits,  when  snow  covered, 
present  striking  contrasts  with  the  sombre  green  of  the 
pine-clad  mountains  and  hills  with  which  thev  are  siir- 
rounded.  It  is  now  known  from  exi)loration  conducted 
by  J.  S.  Diller,  thai  glaciers  of  considerable  size  occupy 
sheltered  valleys  among  the  clustering  summits  of  the 
Three  Sisters. 

Mt.  Hood.  — This  majestic  mountain,  11,225  feet  high, 
is  stated  by  Emmons  to  have  the  most  graceful  outlines 
of  any  of  the  justly  famed  volcanic  peaks  of  the  north- 
west coast.  It  rises  from  the  very  crest  of  the  Cascade 
range,  in  northwestern  Oregon,  and  about  twenty-live 
miles  south  of  the  Columbia  River.  From  the  city  of 
Portland,  it  forms  the  crowning  summit  of  a  far-reach- 
ing landscape.  Something  of  the  grandeur  of  this  moun- 
tain, which  bears  a  similar  relation  to  Portland  that 
Vesuvius  does  to  Naples,  may  be  gathered  from  the 
accompanying  illustration  (Plate  12,  Fig.  A).  Its  lower 
slopes,  as  is  the  case  of  all  the  lofty  peaks  in  Oregon 
and  Washington,  are  densely  forested,  and  form  an  ideal 
setting  for  the  dazzling  cone  rising  above  them.  Could 
an  observer  obtain  a  bird's-eye  view  of  the  Cascade 
Mountains,  they  would  appear  as  a  belt  of  emerald 
studded  at  irregular  intervals  with  immense  brilliants. 

When  the  English  explorer,  Vancouver,  who  gave  Mt. 
Hood  its  name,  first  saw  the  mountain,  he  estimated  its 
height  to  be  at  least  25,000  feet,  and  thought  it  was  per- 
haps the  highest  summit  in  the  world.  Barometric  and 
other  measuroments,  however,  made  by  the  United  States 
Coast  Survey  and  by  the  Fortieth  Parallel  Survey,  have 


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sliown  that  Vancouver's  estimate  was  more  than  twice  the 
actual  height.  In  spite  of  the  corrections  that  prosaic 
measurements  have  iniposed  upon  the  fancy  of  distant 
observers,  Mt.  Hood,  if  not  the  most  lofty,  is,  yet,  in 
the  eyes  of  its  admirers,  one  of  the  most  beautiful  of 
mountains. 

The  summit  of  Mt.  Hood,  like  many  other  similar  peaks 
in  the  same  region,  retains  only  a  portion  of  the  walls  of 
the  original  summit  crater.  It  was  ascended  in  1888  by 
M.  W.  Gorman,  a  member  of  the  mountain  club  (Maza- 
mas)  of  Portland,  who  reports  that  there  are  still  fuma- 
roles  on  the  northeast  slope,  and  steaming  rifts  on  the 
south  side  near  what  is  known  as  Crater  rock,  at  an  ele- 
valion  of  about  8500  feet  above  the  sea.  The  sulphurous 
fumes  from  these  openings  are  sometimes  so  strong  as  to 
be  overpowering,  and  will  discolor  silver  at  a  distance,  in 
the  direction  the  wind  is  blowing,  of  half  a  mile  from 
where  they  issue.  One  peculiar  phenomenon,  shown  on 
Plate  12,  Fig.  B,  is  the  occurrence  of  a  fumarole  in  the 
deeply  snow-filled  crater.  The  actual  summit  of  the 
mountain  consists  of  a  single  block  of  lava  only  a  few 
feet  square,  from  which  one  may  look  down  almost 
perpendicularly  for  thousands  of  feet  on  the  north,  and 
in  other  directions  the  descent  into  the  forests  far  be- 
low is  almost  as  precipitous.  In  the  shelter  of  the  peak 
on  the  north  side,  where  the  walls  circle  round  what  is 
stated  to  have  once  been  a  crater,^  clouds  frequently  col- 
lect even  on  clear  days,  and  from  time  to  time  rise  above 
the  peak  so  as  to  make  it  seem  as  if  steam  was  still  issu- 
ing from  the  summit.      So  deceptive  is  this  appearance 

'  This  great  depression  has  certain  features  which  suggest  that  it  is  an 
amphitheatre  of  glacial  origin. 


i^ 


VOLCANOES  OF  NORTH   AMKRIf.V. 


I'l.ATi:  i; 


Fig.  a.     Mt.  St.  Helen's,  ^Vilsllingtl)ll.     (M.  \V.  (ioniian.) 


Fici.  B.     Mt.  Kiiiuier,  Wasliiiistuii,  Iroiii  the  soutli.     (l'liuli)g!"ii>li  Ity  Brims,  .Seattle.) 


I. 

I  ■  ' 


'i' 


; 

rt  It. 

i 

1 

1 

II!' 

m 


m 

'f'-i  1 


i'i 


-M . 


t 


VOLCANOES    OF   THE    UNITED   STATES 


289 


that  reports  are  fre([ueiitly  iiKide  of  an  eruption.  As 
sliown  by  Arnold  Hague,  who  has  examined  the  sum- 
mit, no  eruptions  have  taken  place  vvitiiin  many  years; 
and  certainly  not  within  the  memory  of  man.  To  jud^^e 
from  a  distant  view,  as  well  as  from  the  reports  of  those 
who  have  trodden  its  dizzy  heights,  it  is  a  typical  example 
of  a  volcanic  mountain  that  has  passed  its  prime  and  is 
slowly  yielding  to  destructive  agencies  of  the  atmosphere. 

It  is  stated  by  George  Gibbs  '  that  stumps  of  trees  occur 
in  abundance  on  the  side  of  Mt.  Hood  above  the  present 
timber  line,  suggesting  that  formerly  the  heat  of  the 
mountain  was  sufficient  to  encourage  the  growth  of  for- 
ests at  an  elevation  which  was  impossible  when  the  moun- 
tain became  cold.  That  this  is  the  true  explanation  of 
the  former  extent  of  timber  growths  seems  doubtful, 
in  view  of  the  antiquity  of  the  later  eruptions  as  de- 
terudned  by  careful  observers  who  have  examined  the 
mountain. 

Mt.  Adams  and  Mt.  St.  Helen's.  —  About  thirty  miles 
north  of  the  Columbia  and  sixty  miles  from  Mt.  Hood, 
stands  Mt.  Adams,  one  of  several  great  mountains  oi 
which  the  people  of  Washington  are  justly  proud. 

Mt.  Adams  is  seen  to  the  greatest  advantage  from  the 
eastward,  as  it  stands  well  to  the  east  of  the  crest  of  the 
Cascade  range.  Several  fine  views  of  its  deeply  trun- 
cated summit  and  of  its  scarred  slopes  were  obtained  by 
the  writer  while  studying  the  geology  of  central  Wash- 
ington, in  1893.  Its  shape  is  that  of  the  frustum  of  a 
cone.  If  its  sides  could  be  prolonged  upward,  they  would 
meet  at  least  a  thousand  feet  above  the  present  flat-topped 
summit.     Whether  the  breadth  of  the  summit  is  due  to 

1  American  Geograpliical  Society,  Transactions,  Vol.  IV,  1874,  p.  So'i. 


•^'W^i^^'' 


240 


VOLCANUKS   OV    NUllTII   AMlilllC'A 


ifh 


the  grctat  size  of  the  original  crater,  to  the  blowing  away 
of  the  top,  or  to  some  other  cause,  has  not  \ievn  deter- 
mined. Although  comparatively  easy  of  ascent,  it  has 
not  received  the  attention  it  deserves,  and  so  far  as  I  am 
aware,  no  competent  observer  has  examined  its  summit. 

On  tlie  west  of  the  Cascade  and  like  Mt.  Adams,  stand- 
ing at  a  distance  from  the  crest  of  that  range,  is  another 
outpost  of  the  mountains,  known  as  Mt.  St.  Helen's.  The 
country  between  these  two  peaks  is  rugged  and  heavily 
forested.  Mt.  St.  Helen's  (Plate  13,  Fig.  A),  in  contrast 
with  its  companion  on  the  east,  has  a  more  regular  conical 
form  and  is  said  to  rise  from  all  sides  to  a,  comparatively 
sharp  apex.  Photographs  of  the  peak  fail  to  sliow^,  how- 
ever, that  it  is  more  regular  or  fresher  in  appearance  than 
its  companion.  Its  reported  conical  form  suggests  that  it 
is  younger  than  Mt.  Adams,  although,  as  mentioned  above, 
the  truncation  of  that  mountain  may  be  due  to  an  explo- 
sion and  not  to  weathering,  in  which  case  its  general  form 
would  not  be  an  index  of  advancing  age. 

If  the  statements  of  frontiersmen  can  be  relied  upon, 
Mt.  St.  Helen's  is  not  only  young,  but  has  been  in  a  state 
of  activity  within  the  past  fifty  years.  Emmons  says  in 
his  essay  on  the  volcanoes  of  the  Pacific  coast,  already 
referred  to,  that  this  mountain  is  the  only  one  in  the 
far  Northwest  concerning  which  he  was  able  to  obtain  a 
definite  account  of  a  recent  eruption.  He  was  told  by  a 
French  Canadian  voyageur,  that  it  was  in  active  eruption 
during  the  winter  of  1841-42.  As  stated  by  the  gentle- 
man referred  to,  the  light  from  the  volcano  at  the  date 
mentioned  was  so  intense  that  one  could  see  to  pick  up 
a  pin  in  the  grass  at  midnight  near  his  cabin,  some 
twenty  miles  distant.      Mr.  Emmons  did  not  visit  the 


jiii 


VOLCANOES   OF   THE    UNITED   STATES 


241 


mountain,  but  states  tliat  with  tlio  aid  of  a  field-glass 
he  could  distinguish  the  ai)parent  track  of  a  lava  How 
which  had  cut  its  way  through  many  miles  of  tiie  forest 
that  clothes  the  mountain's  sides. 

Mr.  M.  W.  Gorman  has  informed  me  that  he  ascended 
Mt.  St.  Helen's  in  1881),  and  found  fumaroles  on  the  north 
east  side,  but  no  steaming  crater,  although,  as  he  states, 
the  volcano  seems  to  have  been  active  in  recent  years, 
and  is  fresher  in  appearance  than  Mt.  Hood.  Lava  has 
flowed  northward  from  the  mountain  for  about  twenty 
miles,  in  some  places  passing  through  a  forest  of  Douglas 
fir,  and  at  certain  localities  cooled  about  large  trees  so  as 
to  take  a  cast  of  their  charred  and  seamed  trunks.  The 
trees  have  since  disappeared,  leaving  well-like  openings 
which  still  remain  unfilled.  Specimens  of  the  lava-casts 
of  the  bark  of  one  of  the  trees  thus  surrounded  has  been 
sent  to  me  by  Mr.  Gorman,  and  is  a  most  interesting 
specimen.  He  states  also  that  in  one  place  the  lava 
dammed  the  end  of  a  canyon  and  led  to  the  formation 
of  a  lake  which  is  still  without  an  outlet.  When  the  last 
eruption  took  place,  the  lava  appears  to  have  flowed  over 
wet  places  and  the  steam  generated,  escaped  at  the  sur- 
face, leaving  what  are  termed  "  blow  holes." 

Mt.  Rainier.  —  For  many  reasons  Mt.  Rainier  is  con- 
sidered by  admirers  of  the  beauties  of  mountain  scenery, 
the  finest  single  peak  in  the  United  States,  not  including 
Alaska.  The  secret  of  its  grandeur  is  not  so  much  its 
exalted  height,  14,525  feet,  although  it  is  the  loftiest 
summit  on  the  northwest  coast,  but  its  isolated  position, 
and  because  it  rises  practically  from  sea  level.  It  is 
one  of  the  few  mountains  in  which  the  visual  height,  or 
the  part  that  rises  above  the  observer,  is   from   many 


mm 


II 


». 


I  I 
I 


ll, 


'i   > 


M 


' 


V 


i 


n « 


I' 


I,   i. 

■   r  '< 


242 


VOLCANOES  OP  NORTH   AMERICA 


points  of  view  nearly  the  same  as  the  actual  elevation 
of  the  suuiniit  above  the  sea.  Mt.  Rainier  is  in  plain 
view  from  Piiget  Sound.  From  the  city  of  Tacoma, 
its  shining  summit  is  wonderfully  attractive  (Plate  14). 
Other  elements  that  combine  to  make  Mt.  Rainier  both 
picturesque  and  sublime  are  the  dense  evergreen  forests 
that  cover  the  country  about  its  base  and  extend  far  up 
its  rugged  side,  the  perennial  snow  that  crowns  its  sum- 
mit, and  its  fine  glaciers  which  descend  far  into  its  encir- 
cling forest. 

The  first  ascent  of  Mt.  Rainier  seems  to  have  been  made 
by  Messrs.  Hazard  Stevens  and  P.  B.  Van  Trump,^  who 
after  many  hardships  reached  its  summit  in  August,  1870. 
In  October  of  the  same  year,  Messrs.  S.  F.  Emmons  and 
A.  D.  Wilson  of  the  United  States  Geological  Exploration 
of  the  Fortieth  Parallel,  also  made  the  ascent.  The  report 
of  this  highly  successful  expedition  contains,  so  far  as  I  am 
aware,  about  all  the  published  observation  concerning  Mt. 
Rainier  that  are  of  value  to  the  student  of  volcanoes.'' 
A  few  selections  from  this  interesting  report  will  enable 
the  reader  to  picture  some  of  the  salient  features  of  the 
magnificent  mountain  which  still  awaits  detailed  explora- 
tion and  careful  study. 

"  Under  the  guidance  of  our  Indians,  a  comparatively 
easy  though  rather  moist  march  of  a  day  and  a  half 
brought  us  finally  on  to  the  crest  of  the  spur  east  of  the 
Cowlitz  River.  As  we  gradually  emerged  from  the  forest 
region  on  tO  the  more  open  ridge,  where  grew  only  isolated 
clumps  of  mountain  fir  and  huckleberry  bushes,  the  rain- 

»  "Atlantic  Monthly,"  Vol.  38,  1876,  pp.  513-530. 

2  S.  F.  Emmons,   "  The  Volcanoes  of  the  United  States,  Pacific  coast," 
American  Geographical  Society,  Bulletin  No.  4,  1876-77,  pp.  31-61. 


:..■*=•-' 


VOLCANOES   OF  THE   UNITED  STATES 


243 


clouils  whioli  had  oiiclosod  us  for  tlio  past  three  days  l)roke 
away,  and  disclosed  another  superb  vie'v  of  tlie  mountain, 
now  (piite  near  us,  and  yet  seemingly  UKjre  lofty  and 
inspiring  than  ever. 

'•  The  details  of  its  surface  were  now  visible.  The  very 
sununit  was  marked  by  a  thin  horizontal  black  line  which 
we  later  found  to  be  the  rim  of  the  crater.  Below  this 
stretched  a  smooth  unbroken  envelope  of  white,  a[)parently 
about  a  third  of  the  way  down ;  then,  at  irregular  dis- 
tances along  its  sides,  peeped  out  black  shoulders  of  rock 
between  which  were  deep  broken  masses  of  glacier  ice, 
looking  like  foaming  cascades  frozen  in  the  instant  of 
their  fall.  This  lower  two-thirds  of  the  peak  was  the 
steepest  of  all,  and  below  it  the  glaciers,  taking  the  form 
of  rivers,  flowed  out  at  more  gentle  angles,  gradually 
hidden  in  their  ever-deepening  beds  between  the  grassy 
spurs."  A  day  or  two  later  the  summit  was  reached. 
''  We  stood  upon  the  edge  of  a  bowl-shaped  crater  of  al- 
most perfect  circular  form,  forming  the  eastern  edge  and 
highest  point  of  the  mountain,  its  interior  filled  to  within 
thirty  or  forty  feet  of  the  rim  with  ice  and  snow,  while 
on  its  outer  slopes  the  blackened  lava,  of  which  it  is  com- 
posed, was  laid  bare  for  a  hundred  feet  or  more  below  the 
summit.  This  was  the  delicate  black  line,  which  we  had 
sometimes  been  able  to  distinguish  from  below,  as  form- 
ing the  summit.  Adjoining  this  on  the  west  was  another 
semicircular  rim  of  rock,  peeping  out  of  the  snow,  the 
remains  of  a  former  crater,  in  the  interior  of  which  this 
more  recent  one  had  built  itself.  It  was  strange  to  see 
even  these  comparatively  small  patches  of  rock  free  from 
the  universal  covering  of  ice  and  snow ;  the  explanation 
first  presented  to  the  mind  was  their  exposed   position, 


h 


■*N«r 


\ 


244 


VOLCANOES   OV   NOUTII   AMERICA 


;!'  I 


1 


and  the  trtMiiundoiiH  force  of  the  wind,  whicli  seemed 
ulniost  sutliL'icnt  to  blow  away  the  rocks.  A  second  was 
soon  seen  in  tho  evidence  of  internal  heat  at  no  great 
dcptli  below  tlie  snrface,  shown  by  countless  jets  of  steam 
and  gas  of  size  from  a  pinhcad  to  an  inch  in  diameter, 
issuing  .iround  the  interior  rim  of  the  crater.  Near  the.se 
j(,'ts  the  hard  rock  is  changcid  into  a  red  clayey  mass  and 
in  front  of  them,  by  the  condensatiim  of  the  steam,  ice 
caverns  have  been  formed,  some  of  sufficient  size  to  admit 
several  persons.  In  one  of  these  we  took  refuge  for  a 
few  moments  t(j  warm  ourselves  and  thaw  our  fingers, 
two  of  mine  being  sli;5htly  frozen.  .   .  . 

"From  our  sunnuit  we  could  see  the  two  other  peaks, 
only  a  few  hundred  feet  lower  than  ourselves,  the  one  to 
the  southwest,  and  the  other  northwest,  from  one  to  two 
miles  distant,  and  separated  by  the  heads  of  a  deep  valley 
filled  by  neve  ice,  which  sloped  rapidly  to  the  westward 
between  the  two  peaks.  It  was  evident  that  this  valley 
was  the  interior  of  a  still  older  and  larger  crater,  of  the 
walls  of  whicli  these  two  peaks  are  the  renmants.  The 
crater  npon  which  we  stood  had  been  built  up  as  an  in- 
terior cone  entirely  within  the  wall  of  this  older  crater, 
and  the  outstanding  pinnacles  of  rock  on  the  east,  which 
we  had  observed  on  our  first  day's  climb  on  the  glaciers, 
must  be  the  >nly  remnant  left  of  the  east  side  of  this 
outer  cone ;  over  a  third  of  the  mountain  mass  had  been 
carried  away  and  that  largely  by  the  energy  of  glacier 
ice. 

"From  the  northeastern  rim  of  the  crater,  we  could 
look  down  on  an  unbroken  slope  of  nearly  10,000  feet  to 
the  bed  of  White  River,  the  upper  half  or  two-thirds  of 
which  was  so  steep  that  one  had  the  feeling  of  looking 


|WiiWh¥iiMWWWiiiliWiifHfr»»B)in«| 


n 


I 


VOrX'ANOES  OF   XOHTH  AMKRICA. 


- 1    •    'v" 


*W* 


»**       ,.;**> 


Mt.  Rainier,  Washington,  from  near  Tacomn,  looking  southeast,  J 


PLATE   14. 


icomn,  looking  soutlienst,  June  14,  1896.     (Photograph  by  A.  H.  Wliite,  Taconia.) 


VOLCANOES   OF   THE   UNITED   STATES 


24o 


over  a  perpendicular  wall.  The  system  of  glaciers,  and 
the  streams  which  flowed  from  them,  lay  spread  out  as 
on  a  map  at  our  feet ;  radiating  out  in  every  direction 
from  the  central  mass,  they  all  with  one  accord  crossed  to 
the  westward,  to  send  their  water  down  towards  Puget 
Sound  or  the  lower  Columbia  River.' 

"  Looking  to  the  more  distant  country,  the  whole 
stretch  of  Puget  Sound,  seeming  like  a  pretty  little  lake 
embowered  in  green,  could  be  seen  in  the  northwest,  be- 
yond which  the  Olympic  Mountains  extended  out  into  the 
Pacific  Ocean.  The  Cascade  Mountains,  lying  dwarfed  at 
our  feet,  could  be  traced  northward  into  British  Columbia, 
and  southward  into  Oregon,  while  above  them,  at  com- 
paratively regular  intervals,  rose  the  ghost-like  forms  of 
our  companion  volcanoes.  To  the  eastward  the  eye 
ranged  for  hundreds  of  miles  over  chain  on  chain  of 
mountain  ridges,  which  gradually  disappeared  in  the  dim 
blue  distance." 

Mt.  Baker.  —  The  most  northerly  of  the  volcanic  piles 
connected  with  the  Cascade  Mountains  south  of  the  United 
States-Canadian  boundary  is  Mt.  Baker.  What  the  char- 
acteristics of  the  north  extension  of  this  volcanic  belt  may 
be,  remains  to  be  discovered,  but  at  present  no  recent  vol- 
canoes are  known  in  the  re";ion  immediately  to  the  north 
of  the  international  boundary. 

Concerning  Mt.  Baker,  little  can  be  said.  It  rises  from 
the  dense  forest  that  extends  from  the  Pacific  coast  east- 

^  An  account  of  these  glaciers  may  be  found  in  "Glaciers  of  Xorth 
America"  by  I.  C.  Russell.     Ginn  &  Co.,  Boston,  1895.    pp.  G2-67. 

The  writer  ascended  Mt.  Rainier,  in  the  summer  of  1896,  and  passed  a 
night  in  one  of  the  craters  at  the  summit.  A  report  on  the  glaciers  visited 
will  be  published  in  the  18th  Annual  Report  of  the  U.  S.  Geological  Su-vey. 
A  popular  account  of  the  expedition  will  .appear  in  "  Scribner's  Magaz'iie." 


I( 


T 


246 


VOLCANOES   OF   NOllTII   AMERICA 


"i» 


ward  to  beyond  the  Cascade  Mountains,  and  is  fully 
twenty-five  miles  west  of  the  crest  of  the  main  range. 
From  Puget  Sound  it  is  in  full  view  on  clear  days  and 
appears  as  a  conical  peak  which  from  its  form  is  at  once 
seen  to  be  of  volcanic  origin.  From  the  north  and  east 
especially  its  summit  appears  to  be  truncated.  Whether 
this  is  due  to  erosion  or  to  volcanic  explosion  has  not  been 
determined. 

Gibbs  ^  states  that  he  v;as  informed  by  officers  of  the 
Hudson  Bay  company  and  also  by  Indians,  that  Mt. 
Baker  was  in  eruption  in  1843,  and  that  "it  broke  out 
simultaneously  with  Mt.  St.  Helen's,  and  covered  the 
whole  country  with  ashes."  It  was  reported  that  during 
this  eruption,  a  neighboring  river,  the  Skagit,  was  ob- 
structed and  all  the  fish  in  it  died,  and  also  that  "  the 
country  was  on  fire  for  miles  around."  The  truth  of 
these  reports  is  to  be  taken  with  some  reserve,  however, 
since  a  fire  on  the  mountain  might  be  mistaken  by  un- 
skilled observers  for  a  volcanic  eruption. 


The  Cascade  Mountains 

The  Cascade  Mountains  extend  from  northern  California 
northward,  with  a  nearly  north  and  south  trend,  across 
Oregon  and  Washington.  At  the  south,  the  range  termi- 
nates in  the  Lassen  peak  volcanic  district,  already  briefly 
described ;  its  northern  extremity  has  not  been  definitely 
ascertained,  but  is  probably  not  far  north  of  Mt.  Baker. 
In  round  numbers,  the  length  of  the  range  is  500  miles, 
and  its  average  width  about  fifty  miles.     In  general,  it  is 

^  George  Gibbs,  "  Physical  Geography  of  the  Northwestern  Boundary  of 
the  Unitea  States,"  American  Geographical  Society,  Journal,  Vol.  IV,  1873, 
p.  358. 


T 


VOLCANOKS    OF   THE    TXITKI)   STATES 


247 


parallel  with  the  coast  line  of  the  Pacific,  120  niilos  dis- 
tant from  the  crest  of  the  range  at  the  south,  and  200 
miles  at  the  north.  The  crest  line,  althou":h  irreiiular 
in  height,  is  in  general  from  5000  to  8000  feet  above 
the  sea,  and  is  broken  by  several  passes,  more  espe- 
cially in  the  northern  half.  The  deepest  gorge,  and  the 
only  one  which  permits  the  drainage  of  the  interior  to 
cross  the  uplift  to  the  Pacific,  is  that  through  which 
Columbia  Ptiver  flows. 

It  is  frequently  stated  or  implied,  that  the  Cascade 
Mountains  are  comjajsed  mainly  of  lava,  and  that  the 
range  owes  its  prominence  to  the  accumulation  of  succes- 
sive sheets  of  this  material,  which  have  flowed  from  vents 
near  the  crest  of  the  range,  and  cooled  and  hardened  so 
as  to  build  up  a  great  ridge.  If  my  understanding  of 
this  hypothesis  is  correct,  the  Cascade  range  is  considered 
to  have  originated  in  much  the  same  way  as  certain  iso- 
lated volcanic  mountains,  like  those  of  the  Hawaiian 
islands  for  example,  in  which  successive  overflows  of 
molten  rock  have  been  piled  one  above  another.  Under 
the  hypothesis  referred  to,  one  is  led  to  infer  that  many 
mountains  of  the  Hawaiian  type  have  been  formed  along 
a  line  of  fissures,  and  that  their  lava  sheets  interlaced  so 
as  to  form  a  much  elongated  ridge.  It  has  been  stated, 
also,  that  the  Cascade  Mountains  differ  from  the  Sierra 
Nevada,  in  that  the  former  have  the  general  structure  just 
mentioned,  while  the  latter  owes  its  leading  features  to 
the  uplifting  and  tilting  of  long,  narrow^  blocks  of  the 
earth's  crust  adjacent  to  faults. 

Although  the  structure  of  the  Cascade  Mountains  has 
not  been  systematically  studied,  and  any  positive  conclu- 
sions in  reference  to  the  mode  of   origin  of   the   range 


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248 


VOLCANOES   OF   NOIITII   AMERICA 


would  be  premature,  yet  there  are  several  facts  known 
whicli  are  inconsistent  with  the  hypothesis  just  stated  and 
point  to  another  explanation. 

During  two  expeditions  conducted  by  the  present  writer 
in  the  region  adjacent  to  the  Cascade  Mountains  on  the 
east,  one  in  Oregon  and  the  other  in  Washington,  the 
eastern  border  of  the  range  was  examined.  The  mono- 
clinal  structure  so  characteristic  of  the  western  portion 
of  the  region,  known  as  the  Great  Plain  of  the  Columbia, 
and  of  its  southern  extension  in  the  Great  Basin,  due 
to  the  tilting  of  fault-blocks,  was  found  to  extend  to 
the  mountains  on  the  west.  As  one  approaches  the 
Cascade  range  from  the  east,  the  tilted  blocks,  the  up- 
turned edges  of  which  are  short  mountain  ridges, 
become  of  larger  size,  and  form  the  immediate  foothills 
of  the  main  range.  This  merging  of  the  structure 
characteristic  of  the  interior  basin  with  the  mountains 
bordering  it  on  the  west,  so  far  as  my  own  observations 
extend,  is  more  pronounced  in  central  "Washington  than 
elsewhere. 

From  what  I  have  seen  of  the  Cascade  Mountains  I 
venture  to  suggest  as  a  working  hypothesis,  that  the  lava 
composing  them,  more  especially  to  the  south  of  Lake 
Chelan  in  Washington,  is  an  extension  of  the  Columbia 
lava  —  described  a  few  pages  in  advance  —  which  covers 
such  a  vast  area  in  the  eastern  portion  of  Oregon  and 
Washington.  This  lava  was  poured  out  in  successive 
sheets  and  afterward  broken  over  extensive  areas,  by 
fractures,  and  the  blocks  thus  formed  tilted  at  various 
angles.  The  hypothesis  here  suggested  assumes  that  the 
Columbia  lava  extended  over  the  Cascade  region  in  origi- 
nally horizontal  sheets,  and  was,  subsequently,  broken  and 


VOLCANOES   OP  THE   UNITED   STATES 


240 


tilted.  Tlie  structure  of  the  Cascade  Jilountains,  under 
this  hypothesis,  is  therefore  not  different  in  its  main  feat- 
ures from  that  of  the  Sierra  Nevada. 

Tlie  Cascade  Mountains  are  not  composed  wliolly  of 
hiva,  as  seems  to  ha  the  prevaihng  idea,  derived  appar- 
ently from  reconnoissance  in  their  soutliern  portion.  Be- 
neath the  lava  in  central  Washington,  there  are  Tertiary 
rocks,  and  highly  metamorphosed  beds  of  unknown  age. 
These  basement  rocks  share  in  the  disturbances  that  have 
affected  the  lavas  resting  on  them.  Much  of  the  nortliern 
portion  of  the  range  is  free  from  lava,  and  differs  in  a 
marked  way  in  all  its  scenic  features  from  tiie  heavily 
lava-covered  portion  to  the  south.  In  the  northern  por- 
tion, the  rocks  are  largely  granite  and  schist,  showing 
at  once  that  to  ascribe  a  volcanic  origin  to  the  range,  as 
a  whole,  is  inadmissible. 

The  great  volcanic  peaks  described  in  the  past  few 
pages  are  of  later  date  than  the  uplifting  of  the  main 
Cascade  range,  and  probably  owe  their  origin  to  the  es- 
cape of  molten  material  through  fractures  formed  at  the 
time  the  mountain  blocks  were  separated  one  from  an- 
other by  fractures,  and  severally  upraised. 

Of  the  two  hypotheses  that  the  reader  now  has  be- 
fore him,  the  first,  namely,  the  one  which  refers  the 
origin  of  the  Cascades  to  volcanic  overflows,  finds  its 
greatest  support  in  the  southern  portion  of  the  range ; 
while  the  second,  or  the  one  that  seeks  to  explain  the 
main  topographic  features  of  the  mountains  by  fracture 
and  upheaval,  applies  more  particularly  to  the  central  and 
northern  portions  of  the  same  mountain  belt.  When  the 
Cascade  Mountains  have  been  thoroughly  explored,  it 
may  possibly  be  found  that  each  of  these  hypotheses  is 


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VOLCANOES   OF   XOUTH    AMEUICA 


in  part  correct,  and  that  the  range  is  less  simple  in  struct- 
ure than  is  now  supposed. 

CoLUMiJiA  Lava 

Merging  with  the  Cascade  Mountains  on  the  east  and 
extending  through  Washington  and  Oregon,  far  into 
Idaho,  there  is  a  vast  lava-covered  country,  which  is 
with(jut  prominent  points  of  eruption.  In  fact,  cinder 
and  lapilli  cones  of  any  description  are  almost  entirely 
absent.  The  boundaries  of  this  lava-covered  region  have 
never  been  traced  except  for  a  few  score  miles  in  north- 
central  and  eastern  ^yashington,  but  it  is  estimated  to 
have  an  area  of  from  200,000  to  250,000  square  miles. 
The  region  most  nearly  comparable  with  it  is  in  India, 
previously  referred  to,  where  the  Deccan  trap  covers  ap- 
proximately the  same  area.  These  two  great  basaltic 
areas  have  also  many  points  in  common  in  reference  to 
the  character  of  the  rocks  composing  them,  the  manner 
in  which  the  lava  occurs  in  sheets  interstratified  with 
lacustral  sediment,  etc.  The  Deccan  trap  is  thought  to 
be  of  Cretaceous,  while  the  Columbia  lava  is  of  Tertiary 
age. 

The  Columbia  lava  is  not  one  vast  flow,  but  is  com- 
posed of  many  independent  sheets,  which  are  sometimes 
separated  by  land  surfaces  containing  the  stumps  of  trees 
and  even  huge  trunks  buried  in  lapilli  and  now  thoroughly 
silicified.  The  lava  sheets  overlap  and  supplement  one 
another  so  as  to  form  a  continuous  and  highly  compound 
system.  No  single  sheet  can  be  traced  over  the  entire 
field,  but  yet  in  the  sides  of  the  numerous  deep  canyons 
that  have  been  eroded  in  the  lava,  individual  flows  can 
frequently  be  followed  for  a  score  or  more  of  miles.     The 


'W^ 


VOLCANOES   OF   TIIK    UNITED   STATES 


251 


series  varies  in  thickness  from  a  few  score  feet  at  cer- 
tain localities  on  its  l)or(lers,  to  over  4000  feet  in  south- 
eastern Washington,  where  it  has  been  (leei)ly  dissected 
l)y  Snake  River,  without,  however,  revealing  its  niaxinnnn 
vertical  extent.  In  the  walls  of  the  canyon  cut  l)y  the 
Cokunl)ia,  according  to  Le  Conte,'  the  aggregate  thick- 
ness of  the  many  lava  sheets  exposed  is  o700  feet. 
Its  average  thickness  is  thcjuglit  by  Symons-  to  lie 
not  far  from  200o  feet.  My  own  observations  suggest 
that  this  estimate  is  too  low,  but  no  conclusion  of  nuich 
value  in  this  connection  can  be  reached  until  more  exten- 
sive surveys  have  been  made. 

Many  sections  of  the  Columbia  lava  were  seen  l)y  me 
in  Washington  and  Oregon,  the  most  instructive  being 
along  the  Columbia  and  Snake  rivers  and  some  of  their 
tributaries  in  Washington.  The  rock  is  usually  a  black 
basalt,  with  frequently  a  well-defined  columnar  struct- 
ure, but  at  times  is  also  highly  vesicular  and  scoriaceous, 
especially  on  the  surface  of  the  sheets.  Many  times 
the  marked  columnar  structure  recalls  the  finest  of  the 
basaltic  columns  so  well  known  at  the  Giant's  Causeway 
and  on  the  Isle  of  Staffa.  The  walls  of  the  canyon  cut 
in  the  lava  are  similar  to  the  Palisades  of  the  Hudson, 
but  are  far  more  extensive  and  usually  exhibit  several 
distinct  colonnades  one  above  another,  which  can  be  fol- 
lowed for  scores  of  miles. 

As  previously  stated,  there  is  a  general  absence  of  cones 
of  eruption  throughout  the  region  covered  by  the  Colum- 
bia lava.     In  view  of   the  original  extent  of   the  lava 


1  "  American  Journal  of  Science,"  Vol.  7,  3d  series,  1874,  p.  168. 

2  "  Report  of  an  Examination  of  the  Upper  Columbia  River,"  Washing 
ton,  1882,  47th  Congress,  12th  Session,  Ex.  Doc.  No.  186,  p.  100. 


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VOLCANOES   OP    NOHTFI    AMKKICA 


westward,  montionod  above,  namely,  that  it  includes  the 
region  of  the  (Jascade  Mountain.s ;  tlie  great  volcanic 
peaks  like  Shasta,  Rainier,  etc.,  nnist  be  considered  as 
points  of  eruption  from  which  some  of  the  lava  flows 
originated.  The  flows  from  these  craters,  however,  arc 
comparatively  small  in  volume,  did  not  spread  widc.'ly, 
and  in  part  are  of  more  recent  origin  than  the  main  body 
of  the  lava  sheets  with  v.hicli  they  are  associated. 

The  absence  of  cinder  cones,  lapilli  craters,  etc.,  over  all 
of  the  region  covered  by  the  Columbia  lava  east  of  the 
Cascade  Mountains,  from  which  the  great  lava  sheets 
could  have  been  derived,  has  led  to  the  conclusion,  first 
suggested,  I  believe,  by  Roichthofer,  that  the  lava  came 
to  the  surface  through  fis.sures,  in  a  highly  fluid  condition 
and  spread  widely  over  the  country  without  forming  vol- 
canic mountains.  This  conclusion  is  sustained  by  obser- 
vation made  by  me  on  the  eroded  edge  of  the  Columbia 
lava,  about  twenty  miles  west  of  Ellensburg,  Washington, 
where  the  border  of  the  lava  has  been  removed  and  a 
deep  valley  formed,  the  eastern  wall  of  which  is  capped 
by  the  lava,  which  rests  unconformably  on  sandstone 
and  shales.  In  the  sedimentary  rocks  beneath  the  lava 
cap,  there  are  large  dikes  that  lead  up  to  and  merge  with 
the  lava  forming  the  surface.  These  dikes  show  that 
the  surface  lava,  in  part  at  least,  came  through  large  fis- 
sures and  spread  out  in  sheets  over  the  land. 

Near  the  upper  surface  of  the  Columbia  lava  in  central 
Washington,  near  Yakima,  there  is  a  thin  layer  of  clay 
formed  as  a  sediment  in  a  Tertiary  lake  and  subsequently 
covered  by  a  lava  flow  a  hundred  feet  thick.  Above  this 
bed  of  basalt  and  resting  evenly  on  its  surface  are  gravels 
and   fine,  evenly  bedded   lacustral   sediments,  having  a 


VOLCANDKS   OF   THE    UNITED   STATES 


2');] 


tliickness  of  125  foot;  next  abovo  is  an  interstratilii'd 
sheet  of  coliininar  basalt,  varyiiii^  from  40  to  lOU  feet 
in  thickness,  which  may  bo  traced  in  an  east  and  west 
direction  for  75  to  100  miles.  Above  this  widely  spread 
sheet  are  lacustral  sediments  known  as  the  John  Day 
system,  whicii  in  places  is  rich  in  the  remains  of  large 
mammals,  showing  it  to  be  of  Tertiary  age. 

Many  sections  of  the  lava  and  of  inters! ratified  lacustral 
sediments,  show  that  a  period  marked  by  great  volcanic 
overllows  ended  in  a  lacustral  period  during  which  an  ex- 
tensive region  to  the  east  of  the  Cascade  Mountains  was 
occupied  by  a  great  lake,  or  perhaps  a  series  of  large 
lakes  of  Miocene  age,  in  whicli  hundreds  of  feet  of  line 
sediments  were  deposited.  These  records  furnish  evidence 
that  the  main  inundations  of  lava  occurred  somewhere 
near  the  middle  of  the  Tertiary  period,  and  not  during 
the  Glacial  epcjch,  as  some  writers  have  supp(jsed.  That 
the  lava  is  of  older  date  than  the  Glacial  epoch  is  also 
shown  by  the  fact  that  in  places  its  surface  has  ])een 
smoothed  and  striated  by  moving  ice  and  is  covered  with 
moraines.  The  lava  does  not  form  a  vast  unbroken  sur- 
face, but,  especially  in  central  Washington  and  in  central 
Oregon,  has  been  disturbed  by  orographic  movements  and 
deeply  dissected  by  streams  since  the  last  addition  of 
molten  rock  was  made  to  the  series.  These  changes  in 
topography  increase  in  extent  as  one  travels  westward 
from  the  eastern  margin  of  the  lava-covered  country  and 
culminate  in  the  Cascade  Mountains. 

In  southeastern  Washington  the  Columbia  lava  has  been 
but  slightly  disturbed  over  an  area  of  several  thousand 
square  miles,  and  furnishes  an  example  of  the  leading 
characteristics  of  the  vast  lava-covered  reoion  of  which  it 


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VOLCANOES   OF   NOKTII    AMEUICA 


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is  a  part,  after  tlu.  final  outpouring  of  niolton  rock  and 
buforo  tlio  ))U{].s  wore  fracturcMl  and  uplicavtMl.  The  lovt'l 
surface  of  the  l)asaltic  plateau  meets  tin;  nioantains  of 
older  rock  in  nuurh  the  .same  maimer  that  th«'  ocean  joins 
a  rugged  and  deeply  iiulented  coast.  The  molten  lava 
entered  the  valleys  and  gave  them  l(!vel  floors  of  basalt ; 
the  deeply  scul[)tured  ridges  between  the  valleys  were 
transformed  into  capes  and  headlands;  outstanding  moun- 
tain peaks  became  islands  in  the  sea  of  molten  rcjck. 
One  of  these  island-like  mountain  peaks,  known  as  Step- 
toe  butte  rises  1000  feet  above  the  surrounding  plateau 
and  is  about  twelve  miles  distant  from  the  shore  of  the 
once  fiery  sea.  Snake  River  tlows  across  the  basaltic  pla- 
teau and  has  excavated  a  magnificent  canyon  some  4000 
feet  deep  and  fifteen  miles  broad.  Within  the  canyon 
there  are  numerous  lateral  ridges  and  a  multitude  of 
striking  architectural  forms  due  to  erosion.  The  excava- 
tion of  the  canyon  has  revealed  the  summits  of  angular 
mountain  ranges  that  were  surrounded  and  finally  buried 
by  the  successive  inundations  of  molten  rock.  One  of 
these  buried  peaks  rises  about  2500  feet  above  the  river 
and  is  covered  by  fully  1500  feet  of  horizontally  bedded 
basalt.  These  are  but  a  few  of  the  facts  that  have  been 
observ^ed  which  demonstrate  the  extent  and  character  of 
the  vast  fissure  eruptions  that  occurred  from  time  to  time 
during  tens  of  thousands  of  years  in  the  far  northwest. 

The  surface  of  the  Columbia  lava  is  covered  with  deep, 
rich,  residual  soil  which  has  resulted  from  the  slow  disin- 
tegration and  decay  of  the  basalt,  and  furnishes  the  mar- 
vellously productive  wheat-lands  for  which  Oregon  and 
Washington  are  justly  celebrated.  In  autumn  the  bound- 
less plateau  is  a  golden  sea  of  waving  grain. 


VOLCANOKM   OF   THE   I'MTKI)   HTATE.S 


255 


• 


Tlio  conditions  prosontcd  on  tin*  eaMtorn  Itorilor  of  tho 
Colimiliiii  liiv.i  in  Idaho,  Jin;  thus  doscrihcd  by  (Ii'ikii':' 
"Wo  found  that  tlu;  older  trachytic  lavas  of  the  hills  had 
biiun  deeply  trenched  hy  lateral  valleys  and  that  these  val- 
leys had  a  lloor  of  the  black  basalt  that  had  been  poured 
out  as  the  last  of  th(!  molten  materials  from  the  now 
extinct  volcanoes.  There  were  no  visible  (rcnies  or  vents 
from  which  these  floods  of  basalt  could  have  jiroeeeded. 
We  rode  for  hours  by  the  margins  of  a  vast  plain  of 
basalt,  stretching  southward  and  westward  as  far  as  the 
eye  could  reach.  It  seemed  as  if  the  plain  had  been 
once  a  great  lake  or  sea  of  molten  rock  which  surged 
along  the  base  of  the  hills,  entering  eveiy  valley,  and 
leaving  there  a  solid  floor  of  bare  black  stone." 

Westward  the  general  conditions  observed  by  Geikie 
extend  through  Idaho,  Oregon,  and  Washington,  but 
the  westward  flowing  streams,  and  particularly  Snake 
River,  have  made  deep  channels  in  the  lava,  so  that 
crossing  it  in  a  straight  line  is  impossible. 

On  the  Great  Plains  of  the  Columbia  in  central  Wash- 
ington, there  are  many  deep  canyons  termed  coulees 
which  have  been  eroded  by  streams,  along  lines  of 
faulting.  The  most  remarkable  of  these,  and  one  of  the 
most  noticeable  topographic  features  of  the  region,  is 
what  is  known  as  the  Grand  Coulee.'^  This  is  a  trench 
across  the  lava  with  vertical  walls  from  300  to  400  feet 
high,  between  which  there  is  a  flat-bottomed  valley,  from 
a  mile  and  a  half  to  four  miles  broad,  occupied  in  part  by 

*  Archibald  Geikie,  "  Geological  Sketches  at  Home  and  Abroad,  1882," 
pp.  337,  338. 

*  The  word  coulee  is  used  in  the  far  Northwest  to  dosiffnate  a  steep-sided 
valley  or  what  in  more  soutli^rii  states  and  territories  would  be  designated 
as  canyons.     Coulee  is  also  used  to  designate  a  lava  flow. 


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256 


VOLCANOES  OF   NOUTH   AMERICA 


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lakes,  some  of  which  are  without  oiitlett?  and  strongly  al- 
kaline. Its  length  from  the  Columbia  River  at  the  north 
to  Coulee  City  is  about  thirty  miles  ;  its  eastern  wall  then 
disappears  and  the  level  lloor  of  the  canyon  merges  with 
the  plain  which  extends  eastward ;  the  western  wall  is 
continued  for  twenty  miles  farther  and  overlooks  a  nar- 
row but  still  wilder  and  more  desolate  vallej^  than  that 
of  the  Grand  Coulee  itself,  which  is  bounded  on  the  east 
l)y  another  vertical  wall  that  begins  just  south  of  Coulee 
City.  The  top  of  the  east  wall  of  the  canyon  tj  the 
south  of  Coulee  City  is  on  a  level  with  the  bottom  of 
the  gorges  to  the  north ;  the  descent  from  one  portion  of 
the  coulee  to  the  other  is  vertical,  and  over  this  rugged 
escarpment  formerly  rolled  a  river  comparable  with  the 
Niagara. 

The  great  coulee  (canyon)  briefly  described  above,  like 
many  others  of  a  similar  nature,  although  of  smaller  di- 
mensions, in  the  same  region,  is  due  primarily  to  a  fault- 
ing of  the  lava,  and  the  enlargement  of  the  break  thus 
formed  by  river  erosion.  Central  Washington  is  now  an 
arid  region  in  which  no  perennial  streams  of  any  consid- 
erable ma<j[nitude  ori^^inate.  Snake  River  flows  across  this 
region  in  a  deep  canyon,  and  derives  its  water  supply  from 
the  mountains  of  Idaho.  Formerly,  however,  the  climate 
was  more  humid  than  at  present,  and  many  streams 
flowed  through  what  are  now  dry  and  desolate  valleys. 
During  the  Glacial  epoch  the  Columbia  in  the  northern 
portion  of  the  great  curve  it  makes  about  the  northern 
border  of  the  Columbia  lava,  was  blocked  by  a  glacier 
that  flowed  from  the  north ;  the  rise  was  thus  held  in 
check  and  escaped  southward  along  the  Great  Coulee, 
and  plunging  over  the  escarpment  in  its  course  near  the 


m 


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VOLCANOES   OF  THE   UNITED   STATES 


257 


present  site  of  Coulee   City  formed  a  magnificent   cata- 
ract.* 

Volcanoes  of  the  Coast  Range 

At  only  a  few  points  in  the  Coast  Mountains  immedi- 
ately bordering  the  Pacific  in  the  United  States,  from  the 
Olympic  Mountains  at  the  north  to  the  Mexican  boun- 
dary, arr»  there  volcanic  rocks  of  recent  origin.  As  the  few 
extinct  volcanoes  that  we  know  in  this  region  furnish  no 
features  not  already  well  illustrr^ted  by  the  examples  pre- 
viously considered,  we  can  pass  them  by  for  the  present 
with  but  a  word. 

Dana^  has  described  an  extinct  volcano  known  as 
Saddle  Mountain,  in  Oregon,  about  fifteen  miles  south 
of  the  Columbia.  This  is  a  crater  now  extinct  and  forest 
covered,  that  is  about  two  miles  wide  and  approximately 
500  feet  deep. 

Muir's  butte  in  California,  south  of  San  Francisco  Bay, 
is  another  prominent  volcanic  pile,  which  has  been  much 
eroded  but  still  retains  the  gracefully  curving  slopes  so 
characteristic  of  cinder  cones. 

Volcanoes  of  the  Rocky  Mountains 

Although  igneous  rocks  are  abundant  throughout  the 
greater  portion  of  the  belt  of  rugged  country  known  as 
the  Rocky  Mountains,  but  a  few  volcanoes  occur  there 

*  An  account  of  the  Big  Bend  country  in  Washington,  and  of  the  west 
central  portion  of  the  region  crossed  by  the  Columbia  lava  may  be  found  in 
"  A  Geological  Reconnoissance  in  Central  Washington,"  by  I.  C.  Russell,  U.  S. 
Geological  Survey,  Bulletin  No.  108.  Reference  to  previous  publications  on 
the  same  region  are  there  given. 

See  also,  I.  C.  Russell,  "  Reports  on  a  Geological  Reconnoissance  in  South- 
eastern Washington,"  U.  S.  Geological  Survey.     In  press. 

2  J.  D.  Dana,  Reports  of  the  Wilkes  Expedition,  "  Geology,"  1849,  p.  644. 


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258 


VOLCANOES   OF   NORTH  AMERICA 


which  are  sufficiently  recent  to  retain  their  characteristic 
topographic  forms.  Much  may  be  learned  in  this  region, 
however,  respecting  the  internal  structure  of  volcanic 
mountains,  and  of  the  nature  of  their  originally  deeply 
seated  roots,  as  they  may  be  termed,  for  the  rea3on  that 
erosion  has  in  many  instances  dis!:ected  these  ancient  piles 
and  laid  bare  their  anatomy. 

Blackfoot  Basin,  Idaho.  —  In  southeastern  Idaho  there 
are  at  least  two  or  three  small  basaltic  craters  which  still 
retain  their  characteristic  shapes  and  are  probably  closely 
associated  in  time  with  the  outflows  of  the  adjacent 
Columl)ian  lava.  As  described  by  A.  C.  Peale,^  one  of 
these  craters  is  a  circular  depression  130  yards  in  diameter 
and  ten  to  twenty  feet  deep.  Surrounding  it  is  a  rim  of 
variously  colored  scoriaceous  basalt  fifty  feet  broad  on  its 
crest.  The  crater  is  of  the  nature  of  a  parasitic  cone, 
possibly  originating  from  lava  flowing  over  water,  and  is 
surrounded  by  a  lava  field.  About  ten  miles  distant  is 
another  similar  crater,  but  not  so  regular  and  less  well 
preserved.  Other  poorly  defined  craters,  together  with 
vesicular  basalt  and  fine  lapilli,  are  mentioned  as  oc- 
curring in  the  same  region. 

Colorado.  —  The  evidence  of  late  volcanic  eruptions  in 
Colorado  is  summarized  by  F.  M.  Endlich  "^  as  follows,  but 
the  weight  of  evidence  seems  to  assign  the  greater  part  of 
the  eruptions  mentioned  to  Tertiary  tim.e  : 

"  A  number  of  isolated  basaltic  eruptions  occur  in 
Colorado.  Prominent  iimong  them  is  that  of  Golden 
City,  where  there  are  table  mountains  composed  of  lig- 


^  Eleventh  Annual  Report  of  the  U.  S.  Geological  and  Geographical 
Survey  of  the  Territories  (F.  V.  Hayden  in  charge),  1877,  pp.  561,  562. 

*  Tenth  Annual  Report  of  the  U.  S.  Geological  and  Geographical  Survey 
of  the  Territories  (F.  V.  Ilayden  in  charge),  1878,  pp.  250,  251. 


VOLCANOES    OF   THE    UNITED    STATES 


2oO 


nitic  beds  covered  with  liiisalt.  Mr.  Marvine  says  with 
regard  tliereto :  '  The  source  of  this  lava  is  from  beneath 
North  Table  Mountain,  on  the  summit  of  which,  and  near 
the  northwest  corner,  the  remnants  of  a  group  of  small 
volcanic  cones  may  still  be  seen;  weather-beaten  and 
nearly  worn  away,  they  still  suffice  to  show  from  whence 
the  lava  came.'  This  explains,  in  a  few  words,  both  the 
source  of  the  basalt  and  the  character  of  such  eruptions. 
Not  %r  from  Golden,  at  Valmont,  a  heavy  dike  of  the 
same  material  may  be  observed.  Inasnuich  as  we  may 
safely  regard  isolated  eruptions  as  the  results  of  local 
dikes  that  have  overflowed,  that  of  Valmont  deserves 
mention  here."  Two  small  basaltic  cones  near  Canyon 
City  are  also  mentioned.  These  have  since  l)een  examined 
by  the  present  writer  and  found  to  be  much  wasted  cinder 
cones,  which  have  lost  the  depressions  that  probably  once 
existed  in  their  summits.  Worn  and  eroded  as  they  are, 
they  appear  to  be  among  the  most  recent  eruptions  to 
the  east  of  the  main  Kocky  Mountain  uplift.  A  few 
other  occurrences  of  basalt  in  Colorado  are  mentioned  by 
Endlich  in  the  report  just  cited,  and  in  conclusion  he 
says :  "Although  the  basaltic  eruptions  have  been  pro- 
ductive of  forms  reseml)ling  crater  cones  more  closely 
than  any  of  the  other  eruptions,  not  one  occurrence  has 
been  observed  in  Colorado  that  could  directly  be  compared 
to  the  cone  and  crater  of  an  active  or  typical  volcano." 

Spanish  Peaks.  —  To  the  student  of  volcanoes,  the  most 
interesting  mountains  in  Colorado  are  the  Spanish  peaks, 
situated  in  the  southeastern  part  of  the  state,  about  sixty 
miles  south  of  Puel)lo.  There  are  two  prominent  peaks 
in  the  group  referred  to,  which  rise  12,720  and  13,620 
feet,  respectively,  above  the  sea,  —  the   adjacent   valley 


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260 


VOLCANOES  OF   NORTH   AMERICA 


has  an  elevation  of  about  5000  feet,  —  and  present  fine 
examples  of  the  ruins  of  ancient  volcanoes.  These  two 
peaks  rise  abruptly  from  a  region  of  comparatively  mild 
relief  and  on  account  of  their  isolated  position  are  im- 
pressive from  whatever  direction  they  are  seen,  not  only 
on  account  of  their  height,  but  because  of  their  sculptur- 
ing and  varied  colors.  They  are  sharp,  conical  peaks 
from  which  radiate  a  large  number  of  narrow,  wall-like 
ridges  formed  by  dikes,  which  mark  the  courses  of  fis- 
sures. These  dikes,  now  weathered  out  so  as  to  stand 
in  bold  relief,  extend  from  the  plain  up  the  mountains 
to  their  very  summits.  Neighboring  volcanic  tablelands 
give  evidence  that  still  other  dikes  and  sheets  of  igneous 
material  have  crumbled  away,  leaving  only  isolated  rem- 
nants. East  Spanish  peak  is  lower  than  its  companion 
and  also  presents  steeper  outlines,  more  sharply  cut  slopes 
and  ridges,  but  less  of  the  characteristic  dike-walls,  than 
its  neighbor.  The  main  body  of  this  beautiful  mountain 
is  composed  of  red  sandstone  that  has  been  altered  by 
heat,  so  as  to  produce  a  number  of  species  of  metamor- 
phic  rocks.  On  ascending  the  western  peak  from  the 
south,  one  passes  over  red  sandstone,  until  near  the  tim- 
ber line  (10.000  feet),  where  large  masses  of  igneous  rock 
are  encountered.  As  described  by  Endlich  :  ^  "  Fragments 
of  numerous  varieties  of  trachyte  and  rhyolitic  trachj'te 
lay  scattered  about  at  the  base  of  the  mountain  in  great 
profusion.  Vertical  places  are  seen  along  the  ridge  we 
propose  to  climb,  and  on  reaching  them  we  find  that  they 
are  caused  by  dikes.  There  are  from  two  to  sixty  feet 
in  thickness  and  not  infrequently  extend  from  near  the 

1  F.  ^I.  Endlich,  Ninth  Annual  Report,  U.  S.  Geological  and  Geographical 
Survey  of  the  Territories  (F.  V.  Hayden  in  charge),  1875,  pp.  129,  133-136. 


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VOLCANOES   OF  THE   UNITED  STATES 


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summit  down  into  the  valley  for  several  miles.  All  the 
strata  in  their  immediate  neighborhood  have  been  baked, 
and  much  metamorphosed.  Near  the  top  of  the  moun- 
tain the  sedimentary  Ijeds  have  totally  disappeared  and 
nothing  remains  but  the  trachyte  brilliant  with  brown 
PMca,  white  oligoclase,  and  long^  shining  needles  of  black 
hornblende.  This  cap  of  igneous  rock  rests  on  the  sedi- 
mentary beds  and,  together  with  the  numerous  radiating 
dikes  and  the  hardening  of  the  sedimentary  layers  by  heat 
and  heated  solutions,  has  preserved  them  from  erosion." 

Evidently  the  highest  summit  of  the  Spanish  peak  is 
a  remnant  left  by  erosion.  The  ancient  volcano  has  been 
completely  removed.  Only  its  roots  remain.  The  west 
peak  contains  more  trachyte  than  its  neighbor,  but  this 
rock  also  rests  on  sandstone,  and  sends  out  a  number  of 
radiating  dikes,  which  descend  to  the  adjacent  plain  as 
conspicuous  ridges. 

Some  of  the  ridges  radiating  from  the  Spanish  peaks 
show  a  remarkably  straight  course,  while  others  follow 
irregular  lines.  Owing  to  the  removal  of  the  sediment- 
ary beds  that  once  enclosed  the  dikes,  the  intruded  rocks 
stand  out  in  bold  relief  and  can  only  be  compared  to 
Cyclopean  walls.  Two  of  these  are  specially  mentioned 
by  Endlich  which  are  eight  and  ten  miles  in  length, 
respectively,  with  vertical  sides,  several  hundred  feet 
high.  In  some  instances  the  hardened  sedimentary  beds 
adjacent  to  the  dikes  also  resist  erosion,  and  each  side  of 
the  central  wall  of  igneous  rock  is  flanked  by  a  somewhat 
gentle  slope  composed  of  sedimentary  beds. 

Transverse  dikes  also  exist  which  cross  those  radiating 
from  the  central  peaks  at  acute  angles.  Ramifications 
also  occur  in  several   instances ;   the  branches  retaining 


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VOLCANOES   OF    NORTH   AMERICA 


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the  same  size,  however,  as  the  dikes  fiuiii  which  they 
diverge.  Wherever  creeks  cross  the  protruding  dikes,  the 
ridges  are  l)roken  through,  but  in  no  instance  have  they 
caused  a  deflection  of  the  lines  of  drainage.  More  than 
lifty  of  the  great  dikes  have  l)een  uiapi)ed,  but  there  are 
many  more  that  are  not  prominent  topographic  features 
and  have  escaped  notice.  Much  more  interesting  and 
instructive  information  concerning  the  remarkable  dikes 
is  contained  in  the  report  cited  above.  In  that  report 
(page  135),  300  or  400  feet  is  given  as  an  estimate  of  the 
amount  of  degradation  over  a  large  area,  as  shown  by  the 
prominence  of  the  dikes  that  now  form  such  a  remarka- 
ble feature  of  the  region.  Students  of  erosion  will  now, 
I  think,  agree  that  these  figures  should  be  greatly  in- 
creased. It  seems  to  the  present  writer,  from  a  study  of 
the  region  adjacent  to  the  Spanish  peaks,  as  well  as  from 
the  descriptions  just  cited,  that  5000  or  6000  feet  would 
be  a  small  measure  of  the  amount  of  surface  material  that 
has  been  carried  away.  The  Spanish  peaks  have  not  only 
been  reduced  to  the  condition  o^  volcanic  necks,  like  those 
of  the  Mt.  Taylor  region.  New  Mexico,  described  on  a 
previous  page,  but  erosion  has  been  continued  until  the 
necks  themselves  have  been  removed,  and  the  ver}'  roots 
of  the  volcano  to  which  they  lead  laid  bare. 

New  Mexico.  —  The  igneous  rocks,  which  on  account  of 
their  influence  on  erosion  form  marked  features  in  the 
relief  of  southeastern  Colorado,  extend  southward  into 
N(  w  Mexico,  and  there  become  even  move  conspicuous. 
Many  tablelands  and  isolated  hills,  or  buttes,  in  New 
Mexico,  owe  their  existence  to  summit  layers  of  lava, 
which  have  sheltered  and  protected  the  sedimentary  rocks 
l)eneatli. 


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VOLCANOES   OF   THE    UNITED  STATES 


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One  of  the  most  conspicuous  of  the  elevated  tablelands 
is  the  Raton  mesa,  situated  in  part  in  Colorado  and  in 
part  in  New  Mexico.  This  nearly  llat-topped  table  rises 
fully  1000  feet  above  the  adjacent  valleys,  and  is  capped 
by  a  layer  of  basalt,  which  breaks  away  at  the  margins  in 
vertical  escarpments,  owing  to  its  columnar  structure  and 
the  slow  removal  of  the  soft  shale  beneath.  Southeast  of 
Raton  mesa  are  other  similar  but  far  more  extensive 
tables,  capped  with  what  was  formerly  an  extension  of 
the  same  lava  sheet.  The  lava  is  a  portion  of  a  widely 
extended  layer,  which  at  the  time  of  its  extrusion  sought 
the  lowest  depression  in  the  surface  over  which  it  flowed. 
From  being  the  flooring  of  a  valley,  it  has,  by  the 
lowering  of  the  country  about  it,  been  left  in  bold  relief. 
Other  examples  of  the  process  by  which  valleys  are 
transformed  into  buttes,  mesas,  and  mountains  attract 
the  eyes  of  the  traveller  in  many  portions  of  the  region 
here  considered. 

One  of  the  few  moderately  recent  volcanoes  in  north- 
eastern New  Mexico  that  have  been  described,  is  Ocate 
crater,  situated  about  thirteen  miles  north  of  Fort  Union. 
This  peak  was  climbed  by  Professor  J.  J.  Stevenson 
and  the  writer  in  1878,  and  found  to  be  a  moderately 
well-preserved  crater  of  basaltic  rock.  It  is  a  truncated 
cone,  with  slopes  of  not  far  from  20°.  Its  symmetry 
has  been  destroyed  on  the  west  side  by  an  overflow  of 
lava,  and  on  the  south  the  rim  of  the  crater  has  been 
breached  by  erosion.  The  cone  is  bare  of  vegetation, 
with  the  exception  of  scattered  tufts  of  grass.  Loose 
fragments  of  lava  are  strewn  over  its  sides.  The  sur- 
face within  the  crater  is  covered  with  scoriaceous  lava, 
but  the  rocks  in  the  walls  show  much  variation  in  text- 


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VOLCANOES  OF  NORTH   AMERICA 


ure  and  color.  A  lava  stream  from  this  crater,  still 
clearly  traceable,  flowed  a  distance  of  five  or  six  miles. 

Ocate  crater  stands  on  a  broad  plain  free  of  basaltic 
lava,  known  in  part  as  the  Ocat<3  mesa,  which  is  similar 
to  Raton  and  neighl)oring  tablelands  to  the  eastward, 
and  is  thought  by  Stevenson  to  be  of  older  date  than  the 
later  eruptions  of  the  crater. 

Another  extinct  volcano  was  discovered  by  Steven- 
son about  seven  miles  east  of  Fort  Union,  and  wholly 
detached  from  the  lava  foiming  the  Ocate  mesa.  This 
crater  is  even  better  preserved  than  the  one  just  de- 
scribed. Its  typical  conical  form  is  well  displayed  and 
its  rim  is  broken  only  by  a  narrow  gap  on  its  north  side. 
The  predominant  rock  is  a  hard,  steel-gray  basalt.  The 
lavas  from  this  crater,  which  is  without  a  special  name, 
flowed  northward  across  the  plain  to  where  Mora  Creek 
had  previously  cut  a  deep  canyon.  The  lava  entered  the 
gorge  and  flowed  as  a  narrow  stream  of  molten  rock 
between  its  precipitous  walls.  This  flow  occurred  at  a 
time  wdien  Mora  canyon  had  been  eroded  to  a  depth  of 
860  feet  below  the  top  of  its  present  walls.  The  moiten 
basalt  poured  down,  filling  the  chasm  to  a  depth  of  400 
feet,  and  entered  the  still  larger  canyon  of  Canadian  River, 
to  which  Mora  Creek  is  tributary,  and  extended  into  it 
for  a  distance  of  three  miles.  Since  the  lava  cooled  and 
hardened,  forming  a  dense  resistant  bed  of  basalt,  the 
river  has  re-excavated  a  channel  through  it,  and  sunken 
to  a  depth  of  230  feet  into  the  rock  beneath.  Some  idea 
of  the  time  rer^uired  for  the  work  can  perhaps  be  appre- 
ciated, when  it  is  stated  that  the  task  performed  is 
many  times  greater  than  that  accomplished  by  Niagara 
River  in  excavating  the  gorge  below  the  falls. 


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VOLCANOES   OF  THE  UNITED   STATES 


205 


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The  lava  in  the  canyon  of  the  Canadian  fonned  a  dam 
which  held  the  water  in  check  and  gave  origin  to  a  lake. 
On  account  of  the  lack  of  sediment  in  the  water  flow- 
ing from  the  lake,  the  erosion  of  the  lava  must  have 
been  exceedingly  slow,  until  the  basin  above  was  filled. 
The  time  required  for  Niagara  to  cut  its  gorge  cannot 
be  determined  with  even  an  approach  to  accuracy,  but 
has  been  variously  estimated  at  from  7000  to  35,000 
years.  The  task  performed  by  the  Canadian  is  much 
greater  than  the  one  Niagara  has  accom])lishcd  and  the 
river  is  far  less  in  magnitude.  There  are  no  facts  avail- 
able for  estimating  the  age  of  the  gorge  in  years,  but  in 
comparison  with  Niagara  it  is  safe  to  say  that  150,000 
to  200,000  years  have  passed  since  the  lava  plunged  in 
a  fiery  flood  into  the  gorge  of  the  Canadian. 

As  the  crater  from  which  this  lava  came  is  still  well 
preserved,  its  rim  being  broken  in  only  one  place,  it  is 
evident  that  a  vast  lapse  of  time  must  have  intervened 
since  neighboring  volcanoes,  like  those  that  have  been 
dissected  to  form  the  present  Spanish  peaks,  for  example, 
were  in  existence.  The  study  of  topographic  forms  thus 
enables  one  to  appreciate,  even  more  vividly  than  the 
study  of  fossil  organic  remains,  the  vast  periods  of  time 
embraced  in  geological  history.^ 

From  a  general  knowledge  of  the  geology  of  New 
Mexico,  gained  by  the  writer  from  travel  and  from  the 
reports  of  various  geological  reconnoissances  that  have 
been  carried  on  there,  it  is  evident  that  much  of  interest 
to  the  student  of  volcanic  phenomena  will  be  found  when 

^  The  craters  briefly  mentioned  above,  and  the  great  volcanic  mesas  of  the 
same  region,  have  been  described  by  Professor  J.  J.  Stevenson,  Vol.  Ill,  Sup- 
plement, "  Geology,"  of  the  Report  of  the  U.  S.  Geographical  Survey  West  of 
the  100th  Meridian  (G.  M.  Wheeler  in  charge),  Washington,  1881,  pp.  167-172. 


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VOLrANOES   OF   NOKTII    AMERICA 


careful  surviiy.s  sliall  liavi;  been  made.  Tlic  many  feat- 
ures of  inten.'st  in  the  n.'gion  studied  l)y  Stevenson  form 
but  a  beginning  of  what  may  be  expected  in  the  future, 
but  at  present  we  shall  have  to  leave  this  exceedingly 
instructive  region,  as  accurate  information  concerning  it 
is  not  available. 

Canada.  —  Kespecting  the  occurrence  of  recent  vol- 
canoes in  Canada,  I  am  unable  to  give  the  student  much 
assistance,  owing  to  lack  of  recorded  information.  It  is 
scarcely  to  be  expected  that  the  volcanic  belt,  lOUO 
miles  broad  in  the  United  States,  ends  abruptly  at  the 
international  boundary,  and  begins  again  in  Alaska,  but 
the  reports  of  surveys  that  have  been  made  in  this  mter- 
mediate  country  contain  but  meagre  accounts  of  recent 
volcanic  phenomena.  The  great  source  of  information 
concerning  the  geography  and  geology  of  the  vast  region 
embraced  in  the  Dominion  of  Canada,  is  the  reports  of 
the  admirable  Geological  and  Geographical  Survey  of 
Canada,  issued  at  Ottawa. 

North  of  the  region  occupied  by  Columbia  lava,  de- 
scribed on  a  former  page,  there  are  vast  areas  drained 
by  Frazer  River,  which  are  covered  with  similar  sheets 
of  basalt  and  in  many  ways  repeat  the  conditions  ob- 
served in  the  region  draine  ^  by  the  Columbia  River. 
Future  exploration  may  possibly  show  that  there  is  a 
great  northward  extension  of  the  Columbia  lava,  but  so 
far  as  can  be  judged,  the  Frazer  River  area  seems  to  be 
distinct.  The  lavas  in  this  region  rest  on  and  are  inter- 
stratified  with  Tertiary  lake  beds,  and  with  beds  of 
lapilli  and  volcanic  dust ;  their  surfaces  are  glaciated 
and  moraine-covered,  thus  showing  that  in  a  general 
way  at  least  they  are  of  the  same  age  as  the  Columbia 


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V0LCAN0K8  OF  THE   UMTKU  HTATKS 


207 


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lava.  Tho  lava  occur  in  .shoots  which  colloctivoly  occupy 
an  area  of  several  tiiousand  scjuaro  niilos,  but  thoir  boun- 
daries liavo  n(!Vor  boon  surveyed.  In  describing  the 
Frazor  River  region,  DawsiMi  states  that  no  distinct  traces 
of  volcanic  craters  were  ol).served,  although  important 
centres  of  extrusion  are  described.'  No  reports  are 
known  of  volcanic  eruptions  in  Canada  within  hist(jric 
times. 

Volcanoes  of  Ala.ska 

In  Alaska,  <and  especially  on  the  Aleutian  islands, 
active  and  recently  extinct  volcanoes  are  so  numerous 
that  an  attempt  to  give  a  detailed  record  of  the  various 
reports  concerning  them  that  have  been  made  would  lead 
to  confusion.  Most  of  the  observations  available  are  of 
what  may  be  termed  a  qualitative  character,  for  the  rea- 
son that  none  of  the  volcanoes  have  been  studied  and  no 
detailed  report  concerning  them  has  been  made.  One  of 
the  most  interesting  volcanic  regions  in  the  world  there 
awaits  exploration. 

Distribution.  —  All  the  active  volcanoes  of  Alaska  are 
on  its  southern  border,  and  with  but  few  exceptions  are 
situated  close  to  the  sea  on  the  Alaskan  peninsula  and 
Aleutian  islands.  The  same  is  also  true,  so  far  as  known, 
of  the  recently  extinct  volcanoes,  with  the  exception  of  a 
number  of  small  ba.saltic  cones  on  the  coast  of  Bering  Sea 
near  St.  Michael,  about  seventy  miles  north  of  the  mouth 
of  the  Yiikon.  So  much  of  Alaska  is  yet  unexplored, 
how^ever,  that  any  statement  concerning  the  absence  of 
extinct  craters  in  the  interior  must  be  received  with 
proper  qualifications. 

^  G.  M.  Dawson,  "  Report  on  Explorations  in  British  Columbia,"  in  Re- 
port of  Progress,  Geological  Survey  of  Canada,  1870-77,  pp.  26,  75-8.3. 


Il 
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268 


VOLCJANOliS    OF    NOHTII    AMKUICA 


Suiillicastcni  Al.i.sUa,  oinhracing  a  great  nuiuber  of 
islauils  that  fringe  tliu  coast  south  of  the  latitude  of 
Mt.  St.  Elias,  is  believed  to  be  almost  entirely  free  of  vol- 
eauie  cones,  with  the  notable  exception  of  Mt.  Edge- 
cunibe,  situated  on  an  island  in  the  vicinity  of  Sitka. 
This  is  rc^ported  to  be  a  basaltic  crater,  2855  feet  high, 
and  to  have  been  in  action  in  170G,  the  only  time  in 
history.'  Mt.  Calder  and  other  peak.s  on  Prince  of  Wales 
Island  are  reported  to  have  been  active  in  1775.  How 
nuich  reliance  is  to  be  placed  on  these  reports,  however, 
which  have  been  .inded  down  from  early  Russian  occu- 
pation, it  is  ditRcult  to  judge,  especially  as  no  reliable 
descriptions  of  the  mountains  n:  jntioned  has  been  made. 

Mt.  St.  Elias,  frequently  stated  to  be  a  volcano  and 
to  have  emitted  steam  at  various  times,  is,  as  ascer- 
tained by  me  during  two  separate  visits,  not  of  volcanic 
origin.  Mt.  Fairweather  resembles  Mt.  St.  Elias  so 
closely  in  outline  that  it  seems  safe  to  assume  that  it  also 
is  non-volcanic.  There  are  no  definite  observations  to 
show  the  presence  of  volcanic  mountains  between  Glacier 
Bay  and  Mt.  St.  Elias,  and  from  distant  views  of  that 
region,  coupled  with  actual  study  of  the  country  for  60 
miles  to  the  west  of  Yakutat  Bay,  I  judge  that  no  vol- 
canoes exist  on  that  portion  of  the  Alaskan  coast.'^ 

The  Aleutian  Volcanic  Belt.  —  The  conspicuous  ^'.nd  in 
fact  the  only  well-characterized  volcanic  belt  in  Alaska 
begins  at  the  east,  at  the  head  of  Cook's  Inlet,  and  extends 
westward  throughout  the  Alaska  peninsula  and  Aleutian 
islands.      This   belt  of  igneous  activity  is   nearly  1600 

1  W.  II.  Dall,  "  Alaska  and  its  Resources,"  Boston,  1870,  p.  467. 
2 "  Second  Ex^-jedition  to  Alt.  St.  Elias,  Alaska,"  U.  S.  Geological  Sur- 
vey, lath  Annual  Report,  1891-92,  pp.  1-91. 


VOLCANOES   OF  THE    INITED  STATES 


200 


niilijs  lon^,  with  a  widtli  in  f^cnoral  of  less  than  forty 
miles.  It  is  so  narrow  and  woll  (U'Hno(i  that  two  parallel 
linos  drawn  on  a  map  of  Alaska,  twc  nty-fivo  niilos  apart, 
may  bo  made  to  im;liid(!  nearly  every  volcano  in  the  bell 
that  is  known  to  have  been  acitiv^e  in  historic  times.  This 
may,  for  convenience.  l)e  termed  iha  Alcutldn  volcanic  belt. 

The  numerous  volcanic  vents  that  mark  the  course  of 
this  lopg,  narrow  belt;  the  many  earthrpiakes  that  hav.: 
been  felt  at  intervals  since  the  discovery  of  Alaska  in  its 
vicinity;  and  many  changes  of  level  recorded  by  terraces 
as  well  as  by  the  observations  of  white  men,  —  all  indicate 
that  a  fracture  or  perhaps  a  series  of  intersecting  breaks 
in  the  earth's  crust  there  exists,  along  which  marked 
changes  have  taken  place  in  recent  times  and  are  prob- 
ably still  in  progress.  The  sea  to  the  south  of  the 
Aleutian  islands  is  deep.  The  deepest  soundings  ob- 
tained previous  to  1896  were  in  that  region,  in  what  is 
known  as  the  Tuscarora  deep.  North  of  the  Aleutian 
islands  lies  Bering  Sea,  for  the  most  part  shallow,  which 
corresponds  with  the  submerged  continental  border  along 
the  Atlantic  coast  of  Nortli  America.  The  conditions 
are  such  as  to  favor  the  view  that  the  Aleutian  volcanic 
])elt  is  not  only  a  belt  of  fracture,  but  that  differential 
movements  of  the  rocks  of  a  pronounced  character,  on  the 
tw^o  sides  of  the  belt,  have  occurred ;  that  is,  it  is  a  belt 
of  faulting.  The  great  faults  in  the  Mt.  St.  Elias  region 
will,  perhaps,  when  traced  westward,  be  found  to  merge 
with  the  fractures  that  have  determined  the  course  of  the 
Alaska  peninsula  and  Aleutian  islands. 

An  outlier  of  the  Aleutian  volcanic  belt  to  the  eastward 
is  Mt.  Wrangell,  on  Copper  River,  200  miles  northeast- 
ward of  the  head  of  Cook's  Inlet.     This  is  a  lofty  volcano, 


(^ 


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«iini,ii.w>'f ■i';W^'^"w^>.i'  uMH«,7i..>|i»'i'<^u<('»''"«'?  ■«i|«i»i<i«fni9>pi>i>nM  jwi|wn«r7Kii^ 


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270 


VOLCANOES  OF   NORTH  AMERICA 


the  height  of  which  has  never  been  accurately  deter- 
mined. Mt.  Wrangell  is  said  to  have  been  in  eruption 
in  1819  ;  and  at  the  time  of  the  most  recent  reports  from 
that  region,  was  still  sending  out  a  column  of  steam 
from  its  summit.  Several  lofty  peaks  in  its  vicinity  are 
probably  also  of  volcanic  origin,  but  this  has  not  been 
definitely  determined. 

It  is  stated  by  Grewingk  ^  that  there  is  definite  infor- 
mation of  volcanic  activity  on  twenty-five  of  the  Aleu- 
tian islands.  On  these  islands,  forty-eiglit  craters  have 
been  enumerated.  In  addition  to  these,  there  are  at 
least  four  on  the  Alaskan  peninsula^  two  on  the  shore 
of  Cook's  Inlet,  one  on  Prince  William  Sound,  and  at 
least  one  —  Mt.  Wrangell  —  on  Copper  River,  making, 
together  with  Mt.  Edgecumbe  and  Mt.  Calder,  fifty-seven 
active  or  recently  extinct  craters.  This  number  will, 
no  doubt,  be  increased  when  detailed  explanations  are 
carried  out. 

Summaries  of  various  reports,  made  largely  by  Russian 
explorers,  concerning  volcanic  eruptions,  earthquakes,  hot 
springs,  etc.,  in  Alaska  have  been  given  by  Dall,^  Gre- 
wingk,^ and  Petroff*;  the  writings  of  these  explorers,  with 
the  exception  of  Grewingk's  travels,  are  easily  accessible. 

Cook's  Inlet. — The  west  coast  of   Cook's   Inlet   rises 


.lyi 


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I 


i  Cited  by  Ivan  Petroff  in  Report  of  Tenth  Census,  Washington,  1884, 
pp.  93-96. 

2  W.  H.  Dall,  "  Alaska  and  its  Resources,"  Boston,  1870,  pp.  286-290, 
466-470. 

'C.  Grewingk,  "Beitrag  zur  Kenntniss  der  orographischen  und  geog- 
nostischen  BeschafPenheit  der  nord-west-kiiste  Amerikas,  mit  den  anliegen- 
deu  Inseln,"  Mineralogical  Society  of  St.  Petersburg,  Proceedings,  1850. 

*  Ivan  Petroff,  "  Report  on  the  Population,  Industries,  and  Resources  of 
Alaska";  in  Reports  of  the  Tenth  Census,  and  of  the  Eleventh  Census, 
Washington,  1881  and  1893. 


In  I 


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VOLCANOES   OF   NORTH   AMERICA. 


ri.ATE   15. 


■   »—>-W^-    l".l         Wf"         11  **"'^'      \V«    '-jpi'-V.^!''  -.--r-.,^^.     .-^ 


fc=,    •• 


Fio.  A.    Fiivloff.  Alaskan  Peninsula.     {Phnt'i<;rapli  by  Lieut.  \.  L.  Broaill)Piit.) 


Fia.  B.    Shishaldin,  Alaska,  from  Berinjr  Sea.    (Photogiai)h  by  L'.  S.  Fish  Conimis- 

siou.) 


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VOLCANOES   OF  THE   UNITED   STATES 


271 


abruptly  from  the  sea  and  has  two  peaks  of  special 
prominence,  known  as  Redoute  and  Iliamna,  both  of 
which  are  volcanic,  and  are  reported  to  be  about  11,000 
and  12,000  feet  high,  respectively.  Iliamna  awakened 
from  a  period  of  repose  in  1778,  and  has  since  kept  in 
a  state  of  mild  activity  with  occasional  explosive  erup- 
tions. In  describing  a  visit  to  Cook's  Inlet,  Dall  ^  re- 
marks that  it  is  only  at  a  distance  of  thirty  or  forty 
miles  that  the  majestic  cone  of  Iliamna  disengages  itself 
from  its  associates  and  stands  revealed  in  all  its  beauty. 
In  the  summer  of  1895,  when  last  seen  by  Dall,  it  was 
sending  out  five  or  six  parallel  columns  of  steam,  and 
seemed  peaceful  enough.  A  few  years  ago,  however,  it 
was  in  violent  eruption  and  discharged  such  a  profusion 
of  hot  dust  and  lapilli  that  the  timber  over  hundreds 
of  square  miles  on  the  adjacent  tableland  was  killed. 
As  in  the  case  of  several  of  the  recently  active  volcanoes 
of  Alaska,  the  steam  rising  from  Iliamna  is  usually  so 
densely  charged  with  volcanic  sand  and  dust  that  it 
appears  black.  For  this  reason,  the  volcanoes  are  usu- 
ally said  to  "smoke,"  although,  in  reality,  little,  if  any, 
smoke  is  present,  but  only  dust-charged  steam.  The 
accompanying  illustration  of  St.  Augustine,  for  which 
I  am  indebted  to  the  United  States  Geological  Survey, 
will  serve  to  show  the  leading  characteristics,  not  only 
of  the  volcanoes  of  Cook's  Inlet,  but  of  several  others 
in  Alaska.  The  timber  line  on  the  west  side  of  Cook's 
Inlet  has  an  elevation  of  about  1000  feet ;  above  that 
limit  is  a  belt  of  alpine  flowers,  which  fade  away  into 
the  desolate  and  frequently  snow-covered  regions  about 
the  mountain's  summits. 

1  W.  H.  Dall,  "  Science,"  Vol.  3,  1894,  p.  92. 


•} ,'/ ..ii:<^ri,'_-^'^'-;  f.  ;• 


-»»f«rt«nw.»»««.wwmi»*»««»l»  ■ 


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272 


VOLCANOES  OF  NORTH   AMERICA 


Redoute  volcano  is  similar  to  its  companion  just  de- 
scribed, but,  so  far  as  I  am  aware,  is  unexplored. 

St.  Augustine.  —  In  the  southern  portion  of  Cook's 
Inlet,  near  the  west  shore,  rises  the  Island  of  St.  Augus- 
tine, consisting  principally  of  a  single  volcanic  cone  of 
striking  grandeur.  (Plate  3,  Fig.  B.)  This  volcano  in 
1880,  as  stated  by  Dall,*  presented  the  appearance  of  a 
low  dome,  about  3800  feet  high,  without  a  peak.  The 
island  on  which  it  stood  was  nearly  circular  in  outline 
and  about  eight  miles  in  diameter.  To  the  northwest, 
it  presented  a  bluff  to  the  sea,  but  sloped  more  gently 
to  the  southeast.  There  are  many  rocks  about  it,  which 
were  formerly  haunted  by  sea  otter.  Previous  to  the 
great  eruption  described  below,  this  island  was  supposed 
to  be  of  volcanic  origin,  but  there  is  no  authentic  record 
of  volcanic  disturbances  having  occurred  upon  it.  In 
August,  1883,  what  is  described  as  "smoke"  was  seen 
to  issue  from  its  summit.  On  the  morning  of  October  6, 
the  inhabitants  of  Alexander  village,  sixty  miles  to  the 
eastward,  heard  a  heavy  report,  and  saw  clouds  and 
flames  issuing  from  the  summit  of  the  island.  The  sky 
became  overcast,  and  a  few  hours  later  there  was  a 
shower  of  pumice  dust.  About  half-past  eight  o'clock 
the  same  day,  an  earthquake  wave,  estimated  at  thirty 
feet  in  height,  rolled  in  upon  the  shore,  deluging  the 
houses  on  the  low  land  and  washing  the  boats  and  canoes 
from  the  beach.  Following  the  first  great  wave,  came 
others  of  less  height.  The  dust  fell  to  the  depth  of 
several  inches,  and  the  darkness  was  so  great  that 
lamps  were  lighted.  At  night,  flames  were  seen  issuing 
from   the  summit   of  the  island,  and  the   snow,  which 

1  "  Science,"  Vol.  3, 1884,  p.  92. 


VOLCANOES  OP  THE   UNITED  STATES 


273 


previously  whitened  it,  disappeared.  After  the  first  dis- 
turbances were  over,  it  was  found  that  the  northern 
slope  of  the  summit  had  fallen  to  the  level  of  the  cliffs 
which  form  the  shore,  and  the  mountain  appeared  as  if 
split  in  two  in  an  east  and  west  direction.  Two  pre- 
viously quiet  volcanoes  on  the  Alaskan  peninsula  began 
simultaneously  to  emit  smoke  and  dust ;  and  in  the  ten- 
fathom  passage  between  Augustine  Island  and  the  main- 
land a  new  island,  approximately  seventy-five  feet  high 
and  a  mile  and  a  half   in  extent,  made  its  appearance. 

In  August,  1895,  Dall  visited  Cook's  Inlet,  and  reports 
that  an  excellent  harbor  for  small  crafts,  which  existed 
on  St.  Augustine  Island  before  the  eruption  of  1883,  has 
been  converted  into  a  placid  lagoon.  A  slender  cloud 
of  steam  ascended  from  the  summit  of  the  volcano, 
which  seems  to  have  been  built  up  by  eruptions  of 
lapilli  and  dust  since  the  explosion  that  rent  it  asunder. 
The  steam  column  serves  as  a  barometer  for  the  sea- 
otter  hunters.  When  it  ascends  undisturbed  by  the 
upper-air  currents  and  spreads  out  aloft  like  the  well- 
known  "  pine  tree "  of  Vesuvius,  the  natives  put  to  sea 
in  their  frail  skin  boats,  or  kyaks,  confident  of  two  or 
three  days  of  fine  weather.^ 

Unimak  Island.  —  This  is  the  first  or  most  easterly  of 
the  Aleutian  islands  and  is  separated  from  the  Alaskan 
peninsula  by  a  narrow  strait,  now  nearly  closed  at  its 
northern  entrance  by  sand  bars.  The  island  is  about 
sixty  miles  long  in  an  easterly  and  westerly  direction,  and 
averages   twenty   miles   in  width.     Its   most   prominent 


I ., 


*  An  account  of  the  eruption  of  Mt.  Augustine,  accompanied  by  a  sketch 
of  the  peak  after  being  split  in  two,  is  given  by  Professor  George  Davidson, 
in  "Science,"  Vol.  3,  1889,  pp.  184-189. 


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274 


VOLCANOES   OF   NORTH   AMERICA 


topographic  features  are  two  volcanic  mountains  which 
are  among  the  most  interesting  and  instructive  in  Alaska. 
The  highest  of  these,  situated  near  the  centre  of  the 
island  and  known  as  Shishaldin,  has  gracefully  curving 
sides  and  rivals  in  beauty  the  far-famed  sacred  mountain 
of  Japan.  Its  summit  is  bare  of  snow,  although  reported 
to  be  from  8000  to  9000  feet  high.  Since  its  first  dis- 
covery by  Russian  navigators,  it  has  been  nearly  always 
in  a  state  of  mild  activity,  as  shown  by  the  steam  ascend- 
ing from  its  summit,  and  occasionally  has  been  the  scene 
of  violent  explosions.  To  navigators  it  is  one  of  the 
most  familiar  landmarks  on  the  Alaskan  coast. 

The  second  volcano,  Pogrumnoi,  on  the  western  portion 
of  Unimak  Island,  is  said  to  be  between  5000  and  6000  feet 
high.  Little  else  is  known  concerning  it,  however,  except 
that  it  has  frequently  been  in  eruption. 

As  stated  by  Petroff,'  Unimak  Island  has  been  and  still 
is  the  theatre  of  the  most  constant  volcanic  activity  in  all 
Alaska.  "Whole  ridges  of  mountain  peaks  have  been 
observed  to  split  open  and  emit  flames,  torrents  of  lava, 
and  clouds  of  ashes.  These  manifestations  were  always 
accompanied  by  the  most  violent  earthquakes,  tidal  waves, 
and  floods,  the  latter  caused  by  the  sudden  melting  of 
masses  of  ice  and  snow  on  the  mountain  tops.  The  great- 
est activity  on  record  occurred  in  1796,  1824,  and  1825, 
and  as  late  as  1827  burning  lava  was  observed  descending 
from  the  craters.  Oonimak  (Unimak)  has  also  from 
time  immemorial  been  the  Aleutians'  great  storehouse, 
from  which  they  obtained  sulphur  and  obsidian,  the  latter 
being  employed  in  the  manufacture  of  knives,  spears,  and 
arrowheads.     The  Russian  missionary,  Veniaminof,  who 

1  Report  on  Alaska  in  Tenth  Census,  1884,  p.  91. 


VOLCANOES   OF  THE   UNITED   STATES 


•JT5 


witnessed  one  of  these  eruptions,  describes  tlie  event  as 
follows : 

"  On  the  10th  of  March,  1825,  after  a  prolonged  sub- 
terranean noise,  resembling  a  heavy  cannonade,  which  was 
plainly  heard  on  the  islands  of  Unalaska,  Akoon,  and 
the  southern  end  of  the  Aliaska  peninsula,  a  low  ridge  on 
the  northeast  end  of  Unimak  opened  in  five  places  with 
violent  emissions  of  flames  and  great  masse.''  of  black 
ashes,  covering  the  country  for  miles  around.  The  ice 
and  snow  on  the  mountain  tops  melted  and  descended  in 
a  terrific  torrent  five  to  ten  miles  in  width  on  the  east 
side  of  the  island.  Until  late  in  the  autumn  the  sea  on 
that  coast  was  turbid  after  this  eruption.  The  Shishaldin 
crater,  which  up  to  that  time  had  also  emitted  flames, 
continued  to  smoke  only,  while  about  midway  between 
summit  and  base  a  new  crater  was  formed,  which  was 
still  smoking  in  the  year  1831.  On  the  11th  of  October, 
1826,  a  small  peak  in  the  interior  of  the  island  opened 
under  violent  explosion  of  fire  and  rain  of  ashes,  which 
covered  not  only  the  southern  end  of  Aliaska  peninsula, 
but  Sannakh  and  Ounga  and  other  adjoining  islands. 
Since  that  time  smoke  comes  out  of  many  places  among 
the  loose  masses  of  rocks  on  the  mountain  side,  and  all 
the  streams  and  ponds  in  the  vicinity  are  hot  enough  to 
emit  steam  in  midsummer." 

From  the  graceful  outlines  of  Mt.  Shishaldin,  shown  in 
the  illustration  forming  Plate  15,  Fig.  B,  reproduced 
from  a  photograph  taken  about  ten  miles  at  sea  to  the 
north,  it  appears  that  the  mountain  is  a  lapilli  cone  built 
principally  of  material  extruded  during  mild  explosions. 
Steam  was  seen  at  the  summit  of  the  mountain  in  the 
summer  of  1895.      So  far  as  known,  no  one  has  ever 


1 


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270 


VOLCANOES  OF   NORTH   AMERICA 


ascended  Shislialdin.  A  study  of  this  splendid  volcano 
would  certainly  be  productive  of  much  valuable  information. 

Bogosloff  Island.  —  In  Bering  Sea,  about  forty  miles 
west  of  the  northern  extremity  of  Unalaska  Island,  and 
in  latitude  53°  58',  longitude  168°  W.,  t.iere  is  an  island 
composed  entirely  of  volcanic  rock  which  has  been  formed 
by  eruptions  within  historic  times.  The  island  is  known 
to  the  Russians  as  loanna  Bogoslova  (St.  John,  the  theo- 
logian) and  to  the  natives  of  the  Aleutian  islands  as 
Agashagok ;  it  is  now  commonly  called  "  Bogosloff." 

Near  the  locality  where  Bogosloff  now  rises,  an  isolated 
rock  was  long  ago  known  to  the  natives  of  the  Aleutian 
islands,  and  represented  on  certain  Russian  charts  bearing 
the  date  of  1768-69.  This  rock  is  mentioned  by  Captain 
Cook,  who  saw  it  in  1778,  and  named  it  Ship  Rock. 

It  is  stated  by  DalP  that  in  1795  the  natives  on  Una- 
laska noticed  what  appeared  to  be  a  fog  in  the  neighbor- 
hood of  the  rock,  which  did  not  disappear  when  the  rest 
of  the  atmosphere  was  clear.  In  the  spring  of  1796,  one 
of  the  natives  more  courageous  than  his  companions 
visited  the  locality  and  returned  in  terror,  saying  that  the 
sea  all  about  the  rock  was  boiling,  and  that  the  supposed 
fog  was  the  steam  rising  from  it.  The  disturbance  was 
accompanied  by  activity  in  the  craters  on  Unimak  and 
Unalaska  islands.  In  May,  1796,  a  considerable  mass  of 
material  was  upheaved  and  the  major  part  of  the  present 
island  was  formed. 

Accounts  of  the  appearance  of  Bogosloff  by  natives  and 
Russian  observers,  cited  by  Dall,  Petroff,  and  others,  do 
not  furnish  ansAvers  to  many  of  the  questions  that  a 
student  of  volcanic  phenomena  would  like  to  ask. 

1"  Science,"  Vol.  3,  1884,  pp.  89-93. 


VOLCANOES   OF  THE  UNITED  STATES 


277 


Unsuccessful  attempts  to  land  on  Bogosloff  were  made 
by  Dall  in  1872,  and  again  in  1873.  The  island  then  had 
a  sharp,  narrow  summit  ridge  about  850  feet  high,  cov- 
ered with  inaccessible  pinnacles,  but  there  was  no  appear- 
ance of  a  crater.  The  shores  were  mostly  precipitous, 
except  at  the  southern  end,  where  the  waves  and  currents 
had  formed  a  small  spit  of  talus,  on  which  a  landing  could 
be  made  in  favorable  weather,  but  the  short  swell  pro- 
duced a  heavy  surf.  When  seen  througli  a  glass,  from  a 
distance  of  four  miles,  the  island  appeared  of  a  light 
purplish-gray  color,  devoid  of  vegetation  or  water,  and 
covered  with  myriads  of  birds. 

In  October,  1883,  a  violent  eruption  occurred  at  Bogos- 
loff,  at  tlie  same  time  that  Mt.  St.  Augustine,  in  Cook's 
Inlet,  was  active.  The  island  was  enveloped  in  steam  and 
a  new  crater  is  reported  to  have  been  formed,  which  has 
since  been  more  or  less  active.  Great  changes  in  the  form 
of  the  island  also  occurred,  and  near  at  hand,  where  a  great 
depth  of  water  was  formerly  reported,  land  was  elevated  to 
a  height  of  nearly  300  feet.  At  the  time  of  the  eruption 
just  referred  to,  a  dark  cloud  of  dust  covered  the  sky 
northward  of  Unalaska  Island  and  hung  near  the  surface 
of  the  sea  for  about  half  an  hour.  It  excluded  the  lisj-ht 
of  the  sun  and  was  accompanied  by  a  rise  of  temperature. 
The  cloud  then  drifted  over  Unalaska,  and  dull  gray  vol- 
canic dust  of  extreme  lightness  fell  in  considerable  abun- 
dance. During  the  eruption,  Makushin,  one  of  the  most 
recently  active  volcanoes  on  Unalaska  Island,  was  quiet, 
although  earthquake  shocks  were  felt.  After  the  erup- 
tion a  new  island  was  discovered  near  the  former  one,  at 
a  locality  where  ships  had  previously  sailed  in  safety; 
and  in  September,  1883,  was  reported  to  be  ''  a  mass  of 


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278 


VOLCANOES   OF    NOllTH    AMEUICA 


fire,"  pn^biibl}'  rod-hot  rooks,  and  steam.  This  new  island, 
situated  lialf  a  nule  nortiiwest  from  "Old  IJogoslotT,"  when 
first  seen  was  conieal  in  shape,  with  an  irregular  outline, 
500  to  SCO  feet  high,  and  about  three-quarters  of  a  mile 
in  diameter. 

BogoslotV  Island  was  visited  by  Lieutenant  J.  C.  Cart- 
well  and  Surgeon  II.  W.  Yemans  of  the  U.  S.  Revenue 
Marine  steamer  Cortvin,  in  1884,  and  many  instructive 
observations  made.^ 

Approaching  the  island  from  the  northeast,  Cartwell 
found  it  to  have  the  appearance  of  being  divided  into 
two  parts  (Plate  IG,  Fig.  A),  the  northern  portion  (New 
Bog(jslott')  being  in  a  state  of  eruption,  and  the  southern 
portion  (Old  Bogoslotf)  a  much  more  serrate  rock  rising 
almost  perpendicularly  from  the  sea,  without  signs  of 
activity.  Between  the  two  and  nearer  the  northern  part 
of  the  New  Bogosloff,  a  tower-like  rock  rises  with  a  slight 
inclination  toward  the  north  to  a  height  of  eighty-six 
feet.  At  a  distance,  the  central  rock  might  easily  be  mis- 
taken for  a  sail  upon  the  horizon,  and  for  this  reason  is 
called  Ship  Rock  or  Sail  Rock.  A  nearer  approach  dis- 
closes the  fact  that  the  two  elevations  are  connected  by  a 
low,  flat  beach,  free  from  rocks,  which  affords  an  excellent 
landing-place  for  small  boats. 

The  narrow  isthmus  connecting  the  two  prominent  por- 
tions of  the  island  is  composed  of  a  mixture  of  fine  black 
sand  and  small  oolitic  stones.  This  isthmus  is  evidently 
of  tlio  nature  of  a  sand  bar  formed  by  the  waves,  of  mate- 
rial washed  from  the  higher  portion  of  the  island;  pos- 

'  Report  of  the  Cruise  of  the  Revenue  Marine  Steamer  Corwin  in  the 
Arctic  Ocean  in  the  Year  1884,  by  Captain  M.  A.  Healy,  U.S.R.M.,  Com- 
mander, Washington,  1889,  pp.  39-44. 


Wk. 


VOLCANOES  OF  THE   UNITED  STATES 


279 


Hibly  a  sllglit  elevjition  is  liuru  rt'conled ;  tlio  nuwur  portiun 
of  the  isljind  IxMiig  at  first  discoiinoctL'd,  as  was  reportud 
by  some  (observers. 

As  related  byCartwell:  "The  sides  of  New  IJogoslolf 
rise  with  a  gentle  slope  to  the  crater.  The  ascent  at  first 
appears  easy,  but  a  thin  layer  of  ashes,  formed  int(j  a 
crust  by  the  action  of  rain  and  moisture,  is  not  strong 
enough  to  sustain  a  man's  weight.  At  every  step  my 
feet  cruslu'd  through  the  outer  covering  and  1  sank  at 
first  ankle-deep  and  later  on  knee-decii)  into  a  soft, 
almost  impali)able  dust  which  arose  in  clouds  and  nearly 
sutt'ocated  me.  As  the  summit  was  reached,  the  heat  of 
the  ashes  became  almost  unbearable,  and  I  was  forced  to 
continue  the  ascent  by  picking  my  way  over  rocks  whoso 
surfaces,  being  exposed  to  the  air,  were  somewhat  cooled 
and  afforded  a  more  secure  foothold. 

"  On  all  sides  of  the  cone  there  are  openings  through 
which  steam  escaped  with  more  or  less  energy.  I 
observed  from  some  vents  the  steam  was  emitted  at  regu- 
lar intervals,  while  from  others  it  issued  with  no  per- 
ceptible intermission.  Around  each  vent  there  was  a 
thick  deposit  of  sulphur,  which  gave  off  suffocating 
vapors."  No  appearance  of  lava  streams  or  of  cinders 
was  noted.  Small  quantities  of  rock  froth,  consisting  of 
unfused  particles  in  a  semi-fused  mass,  were  seen,  but 
during  its  extrusion  the  rocks  do  not  appear  to  have  been 
sufficiently  heated  to  cause  true  fusion. 

A  walk  of  a  third  of  a  mile  along  the  beach  mentioned 
above  brings  one  to  Old  Bogosloff,  where  the  beach 
abruptly  terminates  against  rugged  rocks,  which  rise 
almost  perpendicularly  to  a  height  of  325  feet.  Surgeon 
Yemans  states  that  the  origin  of  New  Bogosloff  was  first 


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280 


VOLCANOES  OF   NOUTII   AMERICA 


made  known  by  Captain  Anderson  of  the  .schooner 
Matthew  Turner,  who  waw  it  on  September  27,  1883,  and 
reported  that  great  volumes  of  steam  and  ashes  were 
erupted  from  tiie  summit  and  also  from  numerous  fissures 
on  the  sides  and  base.  At  night  bright  rellections  from 
the  highly  heated  interior  were  distinctly  visible. 

Samples  of  rock  and  dust  collected  by  the  gentlemen 
whose  reports  have  just  been  cited  were  examined  by 
G.  P.  Merrill  of  the  United  States  National  Museum, 
and  ascertained  to  be  hornblende  andesite.  The  dust  was 
found  to  be  identical  with  dust  that  fell  at  Unalaska, 
sixty  miles  distant,  at  the  time  of  the  eruption.  The 
rocks  are  considered  as  ejected  fragments  of  some  under- 
lying strata  and  not  recent  lava  flows,  thus  confirming 
Cartwell's  observation  in  reference  to  the  absence  of 
molten  lava.  An  account  of  the  ^ineralogical  and 
chemical  composition  of  the  materia  ^x'ming  Bogosloff 
may  be  found  in  "  Science,"  Vol.  4,  1884,  p.  524. 

Although  not  personally  familiar  with  Bogosloff,  I 
venture  to  suggest  from  what  I  have  seen  in  connection 
with  other  volcanoes,  that  the  formation  of  the  island 
was  due  to  the  outwelling  of  viscous  lava,  which  hardened 
at  the  surface  so  as  to  resemble  the  rough,  scoriaceous 
surface  so  common  on  lava  flows.  The  lava,  being  quickly 
cooled,  did  not  flow  as  a  stream,  but  as  in  the  case  of 
some  of  the  Mono  craters  previously  described,  rose  in 
rugged,  scoriaceous  masses,  without  much  explosive  vio- 
lence. Nothing  resembling  a  crater  ring  of  lapilli  and 
dust  is  reported  as  surrounding  the  elevated  crags  of  lava. 

Dall  remarks  that  other  islands  similar  to  Bogosloff  in 
origin  are  known  in  the  same  general  region.*  Mention 
1  "Science,"  Vol.  3, 1884,  p.  92. 


VOLLAXOKS  ol'   NOKIII    AMKliK' A. 


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Fid.  A.     IJoju'osIofT.  Beriiii;  Si-ii,  ISHI.     ( Fli(it(>;;ia|ili  hy  T.  S.  Kisli  ('(imniissioii.) 


Fig.  U.    New  Bogosloff,  Bering  Sea,  1884.    (Photograph  by  I'.  S.  Fish  Commission.) 


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VOLCANOES   OF   THE   UNITED   STATES 


281 


is  made  of  Koniugi  and  Kasdtochi  in  the  western  Aleutian 
chain,  and  of  Pinnacle  Island  near  St.  Matthew's  Island, 
Bering  Sea.  The  last  differs  from  Bogosloff  in  having 
the  crest  deeply  channelled.  It  is  reported  that  light 
has  been  seen  in  the  fissures  of  Pinnacle  Island  "within 
the  last  few  years  by  navigators  passing  in  the  night," 
though  there  is  no  record  of  steam  having  been  noted. 

Unalaska  Island.  —  The  Island  of  Unalaska  is  next  to 
the  largest  and  in  the  development  of  Alaska  the  most 
important  of  the  Aleutian  chain.  It  is  about  120  miles 
long  by  40  miles  wide,  and  has  a  deeply  indented  shore 
line.  Its  borders  are  bold  and  its  surface  exceedingly 
rugged.  Dominating  the  wild,  treeless  landscape  to  be 
seen  while  sailing  along  its  shores,  and  as  observed  by 
the  writer  from  a  steep-pointed  summit  left  by  erosion, 
near  its  northeast  extremity,  stands  Mt.  Makushin,  with 
an  elevation  of  4000  or  5000  feet.  This  mountain  is  of 
volcanic  origin,  although  it  has  not  been  in  active  erup- 
tion, so  far  as  can  be  learned  from  Russian  records  or 
from  the  traditions  of  the  natives,  within  several  genera- 
tions. Steam  still  issues  at  intervals  from  its  summit, 
and  earthquakes  and  subterranean  noises  which  seem  to 
proceed  from  the  mountain  indicate  that  it  should  be 
considered  a  dormant  rather  than  extinct  volcano. 

Petroff  states  in  his  report  in  the  Tenth  Census,  page 
92,  that  Russian  naval  officers  who  visited  Unalaska 
at  long  intervals  in  the  early  part  of  this  century, 
assert  that  many  of  the  points  and  ridges  on  Makushin 
were  observed  to  have  changed  in  outline  owing  to  vol- 
canic action  between  their  several  visits. 

North  of  Makushin  and  in  plain  view  from  the  hills 
about  Iliuliuk,  the  village  usually  visited  by  vessels  bound 


f 


282 


VOLCANOES  OF   NORTH   AMERICA 


I    i 


for  Bering  Sea  and  the  Arctic,  rises  another  conical  vol- 
canic mountain  about  3000  feet  high.  Tliis  volcano  has 
long  been  extinct  and  its  sides  are  scored  with  erosion 
channels. 

Central  and  Western  Aleutian  Islands. — Information 
concerning  the  volcanoes  of  the  Aleutian  islands  is  for  the 
most  part  so  meagre  and  of  such  a  general  nature  that  to 
attempt  to  compile  all  of  it  would  result  in  little  more 
than  a  catalogue  of  names,  with  a  few  dates  at  which 
eruptions  have  been  seen.  Such  compilations  have  al- 
ready been  made  by  Grewingk,  Dall,  and  Petroff,  as  pre- 
viously stated.  As  the  reports  of  these  explorers  are  in 
many  libraries,  it  is  unnecessary  to  republish  the  cata- 
logue of  volcanoes  they  contain. 

On  many  of  the  islands  there  are  volcanic  mountains 
with  craters,  and  deposits  of  lava,  lapilli,  dust,  obsidian, 
etc.,  are  abundant.  Hot  springs  occur  at  many  localities. 
The  general  appearance  of  these  volcanoes  as  seen  from 
the  sea  is  illustrated  by  the  accompanying  photograph  of 
Mt.  Cleveland  on  the  Islands  of  the  Four  Mountains  and 
of  a  similar  cone  known  as  Pavaloff  volcano  on  the 
Alaskan  peninsula.  These  pictures,  together  with  the 
illustration  of  Shishaldin,  will  serve  to  give  some  idea  of 
the  topography  of  the  volcanic  belt  of  southwestern 
Alaska. 

Summary.  —  Meagre  as  is  the  accurate  information  con- 
cerning the  large  number  of  volcanoes  in  southern  Alaska 
and  on  the  Aleutian  islands,  it  is  sufficient  to  show  that  a 
wonderfully  interesting  region  there  awaits  careful  study. 
The  most  instructive  facts  now  in  hand  relate  to  the  dis- 
tribution of  the  volcanic  vents  in  a  well-defined  belt. 
This,  taken   in   connection  with  the   topography  of  the 


:.'*iIj^^\'L^^ii:.S:ixt-ii': 


VOLCANOES   OF  THE   UNITED  STATES 


283 


region,  and  the  records  of  recent  upheavals  as  shown  by 
elevated  beach  line,;,  indicates  that  profound  fractures  have 
there  occurred,  accompanied  by  faulting  and  the  elevation 
of  plateaus,  like  that  bordering  Cook's  Inlet  on  the  west. 
The  geological  structure  in  much  of  southwestern  Alaska, 
so  far  as  can  be  judged,  resembles  that  of  the  Great  Basin  ; 
the  main  geographic  features  being  due  to  the  upheaval 
and  tilting  of  great  blocks  of  the  earth's  crust.  The 
association  of  numerous  active  volcanoes  with  a  narrow 
belt  of  fractures  is  significant,  and,  as  in  Central  America, 
suggests  that  forces  tending  to  break  the  earth's  crust 
when  concentrated  along  narrow  belts  are  able  to  keep 
open  communications  with  the  earth's  highly  heated  in- 
terior, much  more  effectually  than  when  the  disturbances 
affect  a  broader  region,  as  in  that  portion  of  the  Cordilleras 
which  crosses  the  United  States. 

In  closing  this  sketch  of  the  volcanoes  of  North  America, 
I  feel  that  the  impression  obtained  by  the  reader  will  be 
that  a  vast  field  of  great  interest  to  the  student  of  volcanic 
phenomena  has  been  pointed  out,  but  that  our  information 
concerning  it  is  meagre  and  unsatisfactory.  If,  however, 
what  I  have  written  serves  to  stimulate  inquiry  and  en- 
courage fresh  exploration  and  study,  I  shall  feel  more  than 
repaid  for  the  labor  expended  in  compiling  this  book. 


'Ill' 


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CHAPTER  VI 

DEPOSITS  OF  VOLCANO  DUST 

Among  the  important  contributions  of  volcanic  origin, 
made  to  the  surface  of  the  land  over  large  proportions 
of  North  America,  are  certain  deposits  of  fine,  dust-like 
material,  which  was  blown  out  of  volcanoes  m  widely 
separated  regions  and  distributed  over  great  areas  by 
the  wind.  Several  references  to  these  highly  interesting 
accumulations  have  been  made  in  preceding  chapters, 
but  at  the  risk  of  some  repetition,  a  brief  summary 
of  what  is  known  concerning  them  it  is  believed  will  be 
instructive. 

Distribution. — Travellers  in  Central  America  and  Mex- 
ico frequently  refer  to  the  deep,  rich  soils  of  that  region, 
which  consist  largely  of  what  are  usually  termed  vol- 
canic ashes.  Over  extensive  areas  the  soil  is  com- 
posed of  disintegrated  volcanic  rock,  which  grades  on 
one  hand  into  fragments  of  pumice  and  lapilli,  and  on 
the  other  hand  passes  into  fine  volcanic  dust.  Much 
of  this  material  is  known  to  have  resulted  from  the  ex- 
plosive eruptions  of  Conseguina,  Izalco,  JoruUo,  and  other 
volcanoes  that  have  been  in  eruption  since  the  Spanish 
conquest;  but  the  greater  part  of  the  soil-making  vol- 
canic debris  came  from  prehistoric  eruptions. 

Under  the  influence  of  the  moist,  warm  climate,  preva- 
lent in  the  greater  part  of  Central  America  and  Mexico, 

284 


.....^.(r^^.-. 


DEPOSITS  Oi^   VOLCANO   DUST 


285 


the  fine  volcanic  material  strewn  over  the  surface  rap- 
idly decomposes,  and  becomes  available  as  plant  food. 
An  efficient  method  of  natural  fertilization  and  soil- 
renewal  is  thus  illustrated. 

In  the  Sierra  Nevada,  and  over  large  portions  of  the 
Great  Basin,  deposits  of  volcanic  dust  many  feet  in  thick- 
ness are  frequently  met  with.*  These  occur  both  on  the 
surface  and  especially  at  the  mouths  of  gorges  in  the 
uplands,  where  the  dust  has  been  washed  down  and 
accumulated  in  alluvial  cones,  and  interbedded  with  the 
sediments  of  Pleistocene  lakes.  Evidently  the  volcanic 
eruptions  which  furnished  the  dust  occurred  both  in 
Pleistocene  and  Recent  times.  As  explained  in  a  pre- 
vious chapter,  these  deposits  occur  in  great  abundance 
about  the  Mono  craters,  and  have  been  traced  with  con- 
siderable certainty  to  a  distance  of  fully  200  miles  north- 
ward from  them.  Near  the  Mono  craters,  these  deposits 
are  coarse  and  are  mingled  with  gravel-like  lapilli,  but 
become  finer  and  finer,  and  less  and  less  abundant,  with 
increasing  distance  from  their  source.  The  similarity  of 
the  volcano  dust  occurring  at  a  distance — as  in  northern 
Nevada — to  that  found  abundantly  in  Mono  valley,  is  not 
confined  to  physical  properties,  but  embraces  chemical 
composition  as  well.  Analysis  of  volcanic  dust  collected 
in  Truckee  canyon,  near  Pyramid  Lake,  Nevada,  and  of 
the  pumiceous  rhyolite  forming  a  large  part  of  the  Mono 
craters,  shows  an  almost  identical  composition.  The  proof 
is  then  almost  conclusive  that  the  widely  distributed  dust 


bi 


^  I.  C.  Russell,  "  Quaternary  History  of  Mono  Valley,  California,"  United 
States  Geological  Survey,  8th  Annual  Report,  1886-87,  pp.  386,  387.  "  Lake 
Lahontan,"  United  States  Geological  Survey,  Monograph,  Vol.  XI,  1885, 
pp.  146-149. 


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286 


VOLCANOES   OF  NORTH   AMERICA 


came  from  the  same  source  as  the  lava  forming  the  vol- 
canic mountains  in  Mono  valley. 

Dust-like  deposits  of  volcanic  origin  are  of  common 
occurrence  in  Utah,  especially  in  the  vicinity  of  Salt  Lake 
City,  and  attain  a  thickness  in  several  instances  of  from 
thirty  to  fifty  feet  or  more.  Some  of  these  deposits  are 
interbedded  with  lacustral  sediments  of  Tertiary  age ;  but 
others  are  probably  much  more  recent,  although  but  little 
definite  information  concerning  them  is  available. 

Widely  spread  deposits  of  volcanic  dust  occur  over 
great  areas  in  Montana,  South  Dakota,  Nebraska,  and 
Kansas.  Some  of  these  beds  are  of  Tertiary  age,  others 
occur  beneath  fine,  clay-like  material  termed  loess,  of 
Pleistocene  age,  w^hile  still  others  occupy  depressions  in 
the  present  surface,  or  fill  hollows  formerly  occupied 
by  lakes,  and  are  clearly  post-glacial. 

The  deposits  of  volcanic  dust  in  Nebraska,  as  stated  by 
Professor  E.  H.  Barbour,^  have  been  discovered  in  twenty 
counties  which  are  so  situated  as  to  show  that  the  entire 
strata  were  covered  by  the  dust  showers.  These  deposits 
were  formed  after  the  land  had  its  present  topography, 
and  are  coarsest  and  in  greatest  abundance,  being  some- 
times fifty  feet  thick,  in  the  southwestern  portion  of  the 
state,  and  become  gradually  thinner  and  finer  when 
traced  eastward.  This  arrangement  indicates  that  the 
volcano  from  which  the  material  was  deri  ed  is  situ- 
ated to  the  southwestward  of  the  western 


part 


state. 


*  Nebraska  Academy  of  Science,  Vol.  5,  1894-9.5,  pp.  12-17.  In  this 
essay,  illustrations  showing  the  appearance  of  the  dust  when  examined  with 
the  aid  of  the  microscope  are  given,  together  with  drawings  of  the  flakes 
composing  ground  pumice,  for  comparison. 


DEPOSITS   OF   VOLCANO   DUST 


287 


vol- 


of 


As  to  color  and  texture,  some  of  the  Nebraska  deposits 
are  as  pure  and  fine  as  the  best  ground  pumice  of  com- 
merce. From  this  nearly  pure-white  material  there  are 
all  gradations  to  that  which  is  discolored  with  iron  and 
organic  matter,  and  so  coarse  and  mingled  with  so  much 
silt  that  one  cannot  decide  whether  the  dust  or  the 
matter  mingled  with  it  predominates. 

Thick  deposits  of  volcanic  dust  similar  in  nearly  every 
particular  to  that  of  California  and  Nevada,  and  in  the 
region  referred  to  east  of  the  Rocky  Mountains,  occur  at 
numerous  localities  in  Oregon  and  Washington.  Many 
of  these  deposits  contain  the  leaves  of  Tertiary  plants,  or 
are  associated  with  laciistral  sediments  and  lava  flows  in 
such  a  manner  as  to  show  that  they  are  of  Tertiary  age. 
In  some  instances,  however,  accumulations  of  the  same 
kind  of  material  are  found  on  the  surface,  and  in  such 
relation  to  the  present  topography  as  to  demonstrate 
their  recent  origin.  At  a  late  date,  but  not  deter- 
minable in  years,  a  light  shower  of  fine,  pure-white  vol- 
canic dust  fell  on  an  area  of  fully  10,000  square  miles 
in  southeastern  Washington  and  adjacent  states.  This 
deposit  has  been  so  commingled  with  the  soil  that  its 
presence  is  seldom  recognizable,  except  at  the  mouths 
of  ravines  and  gulches  in  the  sides  of  the  valleys,  where 
it  has  been  concentrated  by  small  streams  so  as  to  form 
alluvial  cones.  In  many  such  localitier  a  depth  of  from 
ten  to  twenty  feet  or  more  of  fine,  white,  highly  siliceous 
dust  may  be  seen.  This  last  light  shower  of  dust, 
although  of  slight  importance  in  •  comparison  with  the 
deposits  many  feet  in  thickness  of  older  date,  in  the  same 
region,  yet  in  the  aggregate  added  many  thousands  of 
tons  of  fertilizing  material  to  the  region  over  which  it 


I! 


'i 


H 

'V3 


:| 


■  -"«••»»>•* 


!i5H 


i 

»■■' 


'I 


:    I 


!»' 


li 


'.I 
1 1 


.Will 


III 


nil       I    > 


.'      I 


1- 


288 


VOLCANOES  OF   NORTH  AMERICA 


was  spread.  The  volcanoes'  from  which  the  abundant 
volcanic  dust  deposits  of  the  Pacific  Northwest  were  de- 
rived are  unknown,  but  were  probably  in  the  Cascade 
region.  The  more  recent  dust  showers  may  reasonably 
be  ascribed  to  the  volcanoes  of  which  Baker,  Rainier,  and 
Shasta  are  representatives. 

In  Alaska  and  adjacent  portions  of  Canada,  still  other 
extensive  deposits  of  volcanic  dust  of  recent  date  are 
known.  The  writer,  while  journeying  up  the  Yukon 
River  in  1889,^  observed  above  the  mouth  of  Pelly  River, 
a  conspicuous  white  band  from  eight  to  twelve  inches 
thick,  in  the  upper  portions  of  the  river  terraces,  which 
was  traced  for  fully  200  miles.  This  deposit  of  remark- 
ably pure  volcanic  dust  had  previously  been  noted  in  adja- 
cent regions  and  was  more  fully  examined  by  Hayes  in 
1881.'^  These  various  observations  show  that  it  occupies 
an  area  of  fully  52,280  square  miles,  and  varies  in  thick- 
ness from  a  few  inches  on  its  northeast  border,  to  between 
75  and  100  feet  near  its  southwest  margin.  Its  volume 
has  been  computed  by  Hayes  to  be  in  the  neighborhood  of 
165  cubic  miles.  The  volcano  from  which  this  vast  erup- 
tion of  fine  dust  was  derived  is  as  yet  unknown,  but  from 
its  distribution,  and  its  increase  both  in  thickness  and  in 
coarseness  toward  the  southwest,  the  point  of  eruption 
is  judged  to  be  some  seventy-five  miles  northwest  of 
Mt.  St.  Elias. 

This  Alaskan  deposit  is  pure  white,  except  when  impu- 
rities are  present,  and  indisti.iguishable,  at  least  in  its 

*I.  C.  Russell,  "Notes  on  the  Surface  Geology  of  Alaska,"  in  Geologi- 
cal Society  of  America,  Bulletin,  Vol.  I,  1890,  pp.  145,  146. 

"  C.  W.  Hayes,  "  An  Expedition  through  the  Yukon  District,"  in 
"Natio.ial  Geographic  Magazine"  (Washington,  D.C.),  Vol.  4,  1892,  pp. 
146-150. 


DEPOSITS  OF    VOLCANO   DUST 


280 


physical  properties,  from  the  similar  material  found  so 
abundantly  in  California,  Oregon,  and  Washington.  In 
Alaska,  the  dust  rests  in  part  on  moraines  which  have 
been  abandoned  in  recent  times  by  the  still  retreating 
glaciers,  and  occurs  in  post-glacial  terraces  along  the 
Yukon,  and  is  therefore  of  recent  origin. 

The  great  abundance  of  volcanic  dust  in  the  Cordilleran 
region,  its  wide  distribution,  and  its  occurrence  in  numer- 
ous instances  at  many  horizons  in  the  same  vertical  sec- 
tion, is  evidence  that  vast  areas  in  western  North  America 
have  been  shrouded  in  darkness  at  many  separate  periods, 
and  have  time  and  again  witnessed  horrors  like  those 
which  overwhelmed  Pompeii  and  Herculaneum.  Disas- 
ters similar  to  those  accompanying  the  eruptions  of  Con- 
seguina  and  Krakatoa  occurred  at  intervals  throughout 
the  Tertiary  and  Recent  history  of  fully  one-half  of  North 
America.  Events  of  a  like  tragic  character  are  also 
recorded  by  pre-Carboniferous  deposits  of  volcanic  dust, 
now  consolidated  into  hard  rock,  in  the  Appalachian 
Mountains,  near  Boston,  and  on  the  shores  of  Lake 
Superior.^ 

The  volcanic  dust  of  the  Pacific  states  sometimes  con- 
tains the  bones  of  mammals  and  is  frequently  charged 
with  quantities  of  leaves,  showing  that  some  of  the  tem- 
pests generated  by  volcanic  agencies  were  disastrous  to 
animal  and  plant  life.  These  and  related  disturbances  in 
environment  probably  had  much  to  do  with  the  modifi- 
cation and  extinction  especially  of  the  higher  mai  "aalian 
species. 

Physical  and  Chemical  Properties. — The  leading  physi- 

*  N.  H.  Winchell  and  U.  S.  Grant,  "  Volcanic  Ash  from  the  North  Shore 
of  Lake  Superior,"  in  "The  American  Geologist,"  Vol.  17,  1896,  pp.  211-213. 


.. > \ ILillWMW 


290 


VOLCANOES  OF  NORTH   AMERICA 


cal  characteristics  of  the  volcanic  dust,  referred  to  above, 
are  its  whiteness,  unless  adulterated  with  other  sub- 
stances, and  the  angular  character  of  the  flakes  of  glass 
of  which  it  is  composed.  The  individual  flakes  are  usu- 
ally too  small  to  be  seen  by  the  unaided  eye,  and  in 
nearly  all  respects  closely  resemble  powdered  pumice. 
They  may  be  almost  precisely  duplicated  by  grinding 
ordinary  glass,  or  common  obsidian,  or  pumice,  in  a 
mortar.     When  examined  under  a  microscope,  the  dust 


/^    i^     T=K. 


i     t'l 


^ 


A    ^:=^    -^ 


ijf      <^ 


>^ 


^s^^=:::^  N7    <^ 


V 


^ 


A 


t^ 


^^Q-"  fci 


1.  Volcanic  dust  which  fell  in  Norway,  March  29  and  .TO,  IST.'i. 

2.  Volcanic  dust  emptied  from  Krakatoa,  August  27,  1883. 

3.  Volcanic  dust  from  the  Truckee  River,  Nevada.    Quaternary. 

4.  Volcanic  dust  from  Brakleast  Hill  in  Saugus,  Massachusetts.    Pre-Carboniferous. 

Fig.  11.    Volcanic  dust.    (J.  S.  Diller.) 

is  found  to  consist  of  angular  flakes  and  shreds  of  glass, 
in  which  irregular  cavities  are  frequently  detectable. 
There  is  usually  an  absence  of  crystalline  fragments, 
but  this  is  not  always  the  case. 

The  appearance  of  a  sample  of  volcanic  dust  from 
Truckee  canyon  near  Pyramid  Lake,  Nevada,  which  is 
representative  of  a  large  number  of  similar  deposits 
between  southern  California  and  Alaska,  when  examined 
under   a    microscope,   is    shown   in    the   above   figure, 


|i' 


above, 
ir  sub- 
f  gliiss 
re  iisu- 
xnd  in 
niuiice. 
finding 
i,  in  a 
le  dust 


O*.  V^ 


boniferous. 

f  glass, 
ectable. 
yments, 

st  from 
hich  is 
deposits 
lamined 
figure, 


DEPOSITS  OF    VOLCANO   DUST 


201 


together  witli  drawings  of  similar  material  enii)t('d  by 
existing  volcanoes,  and  also  an  ancient  example  of  like 
origin  but  now  ccmsolidated  into  a  bard  rock,  from  near 
Boston.  This  figure  is  borrowed  from  an  article  by 
J.  S.  Diller,  on  volcanic  sand  which  fell  at  Unalaski,  on 
October  20,  1883.'  In  this  instructive  essa}-,  much  addi- 
tional information  concerning  the  nature  and  origin  of 
the  deposits  under  discussion  may  be  found. 

One  of  the  most  striking  facts  in  connection  with  tiie 
widely  distributed  deposits  of  volcanic  dust  enumerated 
above,  is  their  marked  similarity  in  both  physical  and 
chemical  characteristics.  At  almost  all  of  the  hundreds 
of  localities  examined  by  the  writer  between  Mono  valley 
and  the  Yukon,  the  material  is  a  fine,  white,  highly  sili- 
ceous powder,  which  closely  resembles  pure  infusorial 
earth.  The  only  exceptions  to  be  noted  are  where  the 
deposits  are  impure  on  account  usually  of  the  presence  of 
silt  and  sand ;  this  occurs  especially  when  the  deposits 
are  stratified,  showing  that  in  part  the  material  compos- 
ing them  was  washed  into  lakes  or  other  water  bodies, 
and  when  the  dust  is  mingled  with  larger  fragments 
of  a  similar  origin,  and  grades  into  volcanic  sand  and 
lapilli.  Additional  facts  concerning  what  geologists  term 
jjyrodastics,  that  is  rock  material  reduced  to  fragments 
through  the  agency  of  heat,  may  be  found  in  many  text- 
books of  lithology. 

Although  but  few  quantitative  chemical  analyses  of 
volcanic  dust  deposits  here  considered  are  available,  yet 
it  is  believed,  from  many  qualitative  examinations,  that 
the  two  complete  analyses  given  below  represent  very 
nearly  their  average  composition. 

»"  Science,"  Vol.  3,  1884,  pp.  651-654. 


F 


292 


VOLCANOES  OP  NOttTII   AMEUICA 


ANALYSES  OF   VOLCANIC  DUST 


!l 


if 


I     t 


CONBTITUKNTH. 

No.l. 

No.  2. 

Silica  (SiOa)      . 

. 

.         . 

71.15 

08.01 

Aliiiiiiiiii  ( AI^O.,)  and 

iron  (1 

•ejOs) 

15.1)') 

0.12 

Liiiio  (t'uO) 

0.H5 

3.44 

Magnesia  (Mk<>) 

0.41 

— 

jMangani'se  (MnO)    . 

trace 

— 

I'otash  (K./))    . 

HM 

o.:jo 

Soda  (Na.O)     . 

4.04 

3.00 

Organic  matter 

— 

8.75 

Sulpliuric  acid  (SO.,) 

— 

8.88 

100.57 

00.55 

w: 


No.  1.  From  Truckec  canyon,  Nevada;  analyHi.s  by  T.  M.  Cliatard;  in 
U.  S.  Geological  Siirvoy,  MonograpJi,  Vol.  11,  p.  147. 

No.  2.  From  Nebraska;  analysis  by  11.  II.  Nicholson;  in  Nebraska 
Academy  of  Science,  Vol.  5,  1804-05,  p.  13. 

The  sample  from  Nebraska  is  evidently  less  pure  than 
that  from  Nevada,  as  it  contains  organic  matter  and  prob- 
ably also  sulphate  of  lime,  which  have  been  added  to  the 
material  that  fell  as  dust.  Three  analyses  of  volcanic 
dust  probably  of  Tertiary  age,  from  Montana  and  Idaho, 
published  by  G.  P.  Merrill/  show  from  65.56  to  68.12  per 
cent  of  silica.  The  marked  feature  in  the  composition  of 
the  dust  is  the  high  percentage  of  silica.  Evidently  the 
dust  owes  its  origin  to  the  disintegration  of  acid  lava.  So 
far  as  my  own  observations  extend  and  so  far,  I  believe, 
as  has  been  reported  by  others,  no  deposits  of  volcanic 
dust  of  a  basic  character  have  been  discovered  in  North 
America. 


■il 


1  "Note  on  the  Composition  of  Certain  'Pliocene  Sandstones'  from 
Montana  and  Idaho,"  in  "American  Journal  of  Science,"  Vol.  32,  1886, 
pp. 199-204. 


DEPOSITS   OF   VOLCANO   DUST 


208 


0.30 
3.09 

8.75 
8.88 


The  richness  of  volcanic  dust  in  silica  has  hctMi  noted 
especially  by  Diller,*  who  states  that  in  general  volcanic 
sand  (fine  lapilli)  is  composed  chielly  of  crystalline  frag- 
ments, and  contains  a  lower  percentage  of  silica  than  the 
lava  to  which  it  belongs ;  while  volcanic  dust  contains 
more  silica  than  the  lava  effused  from  the  volcano  from 
which  it  was  derived.  In  explanation  of  these  interesting 
facts,  the  author  just  cited  states  that  "The  difference  in 
chemical  composition  between  volcanic  sand  or  dust,  and 
the  lava  to  which  it  belongs,  appears  to  be  directly  prc^por- 
tionate  to  the  amount  of  crystallization  which  had  taken 
place  in  the  magma  before  its  effusion.  It  is  well  known 
that  crystals  are  frequently,  and  sometimes  abundantly, 
developed  in  a  magma;  so  that,  before  its  extrusion,  the 
magma  may  be  regarded  as  made  up  of  a  crystalline,  solid 
portion,  and  an  amorphous,  more  or  less  fluid  i)ortion. 
These  are  generally  thoroughly  intermingled,  but  occasion- 
ally they  are  arranged,  as  in  obsidian,  in  alternating  bands  ; 
and  they  differ  from  each  other  in  several  important  par- 
ticulars, besides  those  already  mentioned.  The  earliest 
products  of  crystallization  are  basic  minerals,  such  as  the 
ores  of  iron,  hornblende,  and  mica ;  and  as  the  process 
continues,  the  amorphous  portion  of  the  magma  becomes 
more  and  more  siliceous.  On  this  account,  the  crystalline 
portion  of  the  magma  does  not  contain  as  high  a  percent- 
age of  silica  as  that  which  is  amorphous.  In  the  process 
of  crystallization  the  gases  absorbed  in  the  magma  are 
rejected  from  the  crystallizing  substances,  and  accumulate, 
under  enormous  tension,  in  the  portion  which  is  amor- 
phous. In  this  manner  the  non-crystalline  portion  of 
the   magma   becomes  stored  with  explosive  compounds, 

1  J.  S.  Diller,  "  Science,"  Vol.  3,  1884,  pp.  053,  051. 


i. 


B^r»^s^5^5=r7!= 


-  •■•*  ti'^mtf'^tftfm 


^f 


294 


VOLCANOES  OF  NORTH  AMERICA 


'I     i 


111! 


in     -i 


under  such  stress,  that  when  the  pressure  is  relieved, 
they  may  blow  it  to  line,  siliceous  glass-dust;  while  the 
crystalline,  solid,  basic  portion  of  the  magma,  pulver- 
ized rather  by  external  than  internal  forces,  is  '  iduced 
to  sand." 

Among  the  illustrations  of  the  fact  that  volcanic  dust 
is  frequently  richer  in  silica  than  the  parent  lava,  the  com- 
position of  the  material  discharged  by  Krakatoa,  in  1883,  is 
cited.  The  dust  resulting  from  that  eruption,  and  widely 
distributed  over  the  earth,  has  been  found  to  contain  65.04 
per  cent  of  silica ;  v/hile  the  lava  effused  at  the  same  time 
contains  but  62  per  cent  of  silica. 

The  abundant  occurrence  of  acid  volcanic  dust,  and  the 
fact  that  basic  material  of  a  similar  physical  character  has 
not  been  found  in  the  deposits  under  consideration,  is 
apparently  not  fully  explained,  however,  by  the  hypothesis 
just  quoted.  In  addition  to  the  changes  produced  in  a 
magma  by  fractional  crystallization,  it  may  bo  suggested 
that  the  chemical  composition  of  the  magmas  as  a  whole, 
from  which  the  dust  was  derived,  plays  an  important 
part.  Acid  magmas,  as  stated  in  a  previous  chapter, 
are  of  different  fusibility,  and  generally  form  viscous 
fluids ;  while  basic  magmas  are  more  easily''  fused  and 
form  more  perfect  fluids.  The  viscous  magmas,  when 
expanded  by  occluded  steam  and  gases,  become  brittle  on 
the  loss  of  a  small  amount  of  heat,  and  are  in  a  condition 
to  be  shattered ;  wh\le  the  more  fluid  magmas  allow  the 
occluded  steam  and  gases  to  escape  without  violent  explo- 
sions. This  suggestion  is  in  harmony  with  the  well-known 
fact  that  most  pumice  is  rich  in  silica. 

While  eruptions  of  basic  magmas  may  form  large  quan- 
tities of  lapilli,  and  yield  dust  particles  by  the  attrition 


DEPOSITS   OF   VOLCANO   DUST 


295 


of  projected  fragments,  the  proportion  of  dust  due  to  the 
explosion  of  occluded  steam  would  be  comparatively  small ; 
on  the  other  hand,  siliceous  and  usually  viscous  magmas 
would  be  shattered  by  the  explosion  of  the  steam  con- 
tained in  them,  and  give  origin  to  an  al)undance  of  dust- 
like particles.  The  presence,  therefore,  of  vast  accumula- 
tions of  siliceous  volcanic  dust,  and  the  absence  of  basic 
material  of  similar  nature  in  the  Cordilloran  region,  is 
rather  to  be  accounted  for  by  the  fact  that  volcanoes 
effusing  acid  lava  manufacture  vastly  more  dust  particles 
than  those  from  which  only  basic  lavas  are  extruded. 
The  fractional  crystallization  that  takes  place  in  cooling 
magmas  cited  by  Diller,  while  no  doubt  an  important 
factor  favoring  the  production  of  acid  volcanic  dust, 
seems  too  delicate  an  adjustment  to  alone  account  for 
the  vast  abundance  of  acid  volcanic  dust  and  the  ab- 
sence of  basic  material  of  like  character  over  a  large 
portion  of  North  America.  In  Oregon  and  Washington, 
for  example,  the  igneous  rocks  that  occur  in  greatest 
abundance  are  of  the  basic  type,  while  all  of  the  dust 
deposits  known  are  rich  in  silica.  Rather  tb  m  expect 
that  a  basic  magma  like  that  producing  basalt  could,  Ijy 
fractional  crystallization,  give  origin  to  highly  acid  dust, 
it  seems  more  rational  to  assume  that  the  Ijasic  lavas 
came  from  different  eruptions  than  the  volcanic  dusts  so 
abundantly  associated  with  them. 

Economic  Importance.  —  Volcanic  dust  is  used  as  an 
abrasive  principally  in  the  form  of  polishing  powder 
and  as  an  ingredient  in  friction  soap.  It  is  serviceable 
for  most  if  not  all  of  the  uses  for  which  ground  pumice 
and  diatomaceous  earth  are  employed.  Experiments  have 
shown  that  it  may  be  used  with  satisfactory  results  in 


■MMHMMBid»i»ii«IH«n«feli 


P0> 


Mt 


fj 


K 


(I 


'II 


I 


'l,i 


II 


h 


uil\ 


%\ 


I! 


ii  '  ! 


i 


.:i 


!       ! 


296 


VOLCANOES   OF   NOliTH   AMERICA 


connection  with  paint  as  a  substitute  for  sand  in  cer- 
tain processes  of  painting,  particularly  when  the  surface 
coated  is  exposed  to  the  weather.  Other  uses  for  this 
abundant  and  remarkably  clear,  white,  siliceous  powder 
will  no  doubt  be  found. 


CHAPTER  VII 


THEORETICAL  CONSIDERATIONS 


li'> 


All  modern  theories  that  have  been  advanced  to  ac- 
count for  volcanic  phenomena  rest  on  still  other  and 
more  general  theories  in  reference  not  only  to  the  condi- 
tion of  the  interior  of  the  earth,  but  to  the  origin  of  the 
earth  itself. 

The  meteoric  hypothesis  of  Lockyer,  which  may  be  con- 
sidered as  a  modification  of  the  earlier  nebular  hypothesis 
of  Laplace,  more  nearly  satisfies  the  facts  observed  in 
reference  to  the  present  condition  and  to  the  origin  of  the 
earth,  than  any  other  explanation  that  has  been  advanced, 
but  cannot  be  considered  as  entirely  satisfactory.  With- 
out attempting  to  discuss  the  profound  problems  referred 
to,  we  will  assume,  for  the  present,  that  the  earth  reached 
its  present  condition  after  a  long  period  of  cooling  from  a 
molten  condition,  during  which  a  cool  and  solid  crust  was 
formed  about  a  still  highly  heated  interior. 

Internal  Heat  of  the  Earth.  —  As  is  well  known,  there 
are  abundant  observations  to  show  that  diurnal  changes 
of  temperature  do  not  affect  the  earth  below  a  depth  of 
about  three  feet ;  while  seasonal  changes  of  temperature 
do  not  occur  below  an  average  depth  of  about  forty  feet. 
Any  temperatures  that  the  earth  may  have  below  this 
depth,  therefore,  cannot  be  due  to  the  radiant  energy  of 
the  sun.  Below  the  depth  in  the  earth  to  which  the  in- 
fluences of  seasonal  changes  are  felt,  there  is,  as  shown  by 

297 


II 


I  ! 


298 


VOLCANOES   OF   NORTH   AMEUICA 


1  ; 


I     ! 


•15 


obseivation,  a  zone  of  invariable  temperature,  below  which 
the  temperature  increases  in  general  at  the  rate  of  one 
degree  Fahrenlieit,  for  each  fifty  or  sixty  feet  of  descent. 
At  this  rate  of  increase,  a  temperature  of  212°  would 
be  reached  at  a  depth  of  about  8000  feet.  At  a  depth 
of  thirty  miles  the  temperature  would  be  such  that  all 
known  substances  would  melt  under  ordinary  atmospheric 
pressure.  The  measurements  on  which  these  well-known 
conclusions  are  based  do  not  extend  below  a  depth  of 
approximately  one  mile,  but  are  sustained,  at  least  in  a 
qualitative  way,  by  the  phenomena  observed  in  volcanoes 
and  hot  springs.  The  accepted  conclusion  is  tluat  the 
interior  of  the  earth  below  a  depth  of  a  very  few  thousand 
feet  is  intensely  hot. 

Computations  made  by  Tate,  based  on  the  observed 
rate  of  increase  of  temperature  towards  the  centre  of 
the  earth,  and  the  rate  at  which  rocks  conduct  heat, 
have  shown  that  the  internal  heat  of  the  earth  is  being 
carried  away  and  dissipated  in  space  at  the  rate  of 
250  units  of  heat  per  annum  per  square  foot  of  the 
earth's  surface ;  the  unit  of  heat  used  being  the  amount 
of  heat  necessary  to  raise  the  temperature  of  one  pound 
of  water  one  degree  Fahrenheit.  The  computed  annual 
loss  of  heat  from  each  square  foot  of  the  earth's  surface 
is  sufficient  to  warm  one  and  one -fourth  pounds  of  water 
from  the  freezing  to  the  boiling  point.  If  we  accept 
the  conclusion  of  Laplace,  Lockyer,  and  others,  —  that 
the  earth  was  formerly  in  a  molten  condition,  —  it  fol- 
lows that  the  rate  at  which  the  earth  has  been  losing 
heat  was  formerly  greater  than  now,  and  that  it  will 
continue  to  decrease  in  the  future.  Another  inevitable 
conclusion  is  that  this  loss  of  heat  has  been  accompanied 


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THEOllETICxVL    CONSIDKllATIONS 


209 


by  contraction.  The  earth  is  smaller  than  formerly  and 
will  continue  to  decrease  in  size. 

Condition  of  the  Earth's  Interior. — The  observed  in- 
crease in  temperature  with  depth  in  the  earth  naturally 
lead  to  the  supposition  that  the  interior  is  in  a  molten 
condition ;  but  when  the  influence  of  pressure  on  the 
fusing  point  of  rocks  was  considered,  it  became  ques- 
tionable whether  any  portion  of  the  interior  could  exist 
in  a  liquid  condition. 

Astronomers  have  shown  conclusively,  as  it  appears, 
that  the  earth  behaves,  in  reference  to  the  attraction  of 
the  sun  and  moon,  like  a  rigid  sphere ;  the  conclusion 
being  that  the  earth  is  as  rigid  as  a  sphere  of  steel  of 
the  same  dimensions. 

Geological  observations  have  proven  conclusively  that 
the  earth's  surface  is  continually  in  motion.  Portions 
of  the  surface  are  undergoing  elevation,  while  other  por- 
tions are  being  depressed.  The  proof  is  abundant,  also, 
that  similar  movements  have  been  in  progress  since  the 
dawn  of  geological  history.  The  differential  mo^  eraents 
of  adjacent  areas  in  numerous  instances  are  measured  by 
tens  of  thousands  of  feet. 

These  apparently  opposite  conclusions  reached  by  as- 
tronomers and  geologists  may  be  harmonized  on  the 
hypothesis  that  the  interior  of  the  earth,  although  highly 
heated,  is  solid  by  reason  of  the  pressure  to  which  the 
rocks  composing  it  are  subjected,  but  that  they  would 
become  plastic  or  even  highly  fluid  if  the  pressure  was 
sufficiently  relieved.  This  condition  of  the  earth's  in- 
terior is  expressed  by  the  term  potentlalhj  plastic;  that 
is,  the  material  of  which  it  is  composed  is  solid  by  rea- 
son of    the    pressure  under  which    it   exists,   but   would 


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300 


VOLCANOES   OP  NORTH  AMEUICA 


become  plastic,  by  reason  of  its  heated  condition,  if  the 
pressure  were  relieved.  In  brief,  the  conception  of  the 
condition  of  the  earth  that  is  in  harmony  with  the  con- 
clusions reached  by  both  astronomers  and  geologists  is, 
that  it  consists  of  a  comparatively  thin,  rigid  shell, 
termed  the  earth's  crust,  enclosing  a  highly  heated  and 
solid,  but  potentially  plastic,  sphere,  —  the  passage  from 
one  to  the  other  being  gradual.  The  inner  sphere  sus- 
tains the  pressure  of  the  outer  shell,  or,  more  accurately, 
pressure  increases  Avith  depth ;  but  if  pressure  is  suffi- 
ciently relieved  on  a  portion  of  the  heated  interior,  it 
will  at  once  become  plastic  or  liquid,  and  in  a  condition 
to  flow  under  moderate  pressure. 

Changes  on  the  earth's  surface  —  such  as  the  removal 
of  material  from  one  locality  to  another,  through  the 
action  of  rivers,  etc.  —  lead  to  changes  in  the  pressure 
of  the  crust  on  the  potentially  plastic  interior,  and  tend 
to  change  its  shape.  Contraction,  accompanying  loss  of 
heat,  decreases  the  size  of  the  inner  sphere,  and  the  rigid 
crust  has  to  adjust  itself  to  the  shrinking  mass  within ; 
this  it  does  by  folding  or  bending,  and  by  fractures  and 
the  overthrusting  or  underthrusting  of  the  rocks  on  the 
sides  of  the  break.  Accompanying  these  changes  are 
both  regional  and  local  elevations  and  depressions  of  the 
earth's  surface. 

A  fracture  in  the  earth's  crust,  if  it  reached  from  the 
surface  to  the  highly  heated  interior,  would  be  equiva- 
lent to  a  relief  of  pressure.  The  highly  heated  and 
potentially  plastic  rocks  in  the  vicinity  of  such  a  fract- 
ure would  at  once  become  plastic  or  even  highly  fluid, 
and  be  forced  into  the  break  by  the  pressure  of  adjacent 
rocks.     When  the   pressure  was  sufficient  to   force   the 


THEOUETICAL   CONSIDKUATIONS 


301 


molten  material  to  the  surface,  volcanic  plicnomona 
would  ensue.  Before  testing  this  hypothesis,  other  facts 
concerning  the  earth's  crust  should  be  considered. 

Intrusive  Rocks.  —  Observations  in  many  regions  have 
shown,  as  stated  in  tlie  first  chapter  of  this  book,  that 
fractures  have  occurred  in  the  earth's  crust  at  many 
different  geological  periods,  and  been  injected  with 
molten  rock  which  has  been  forced  into  the  fissures 
from  below.  Fissures  filled  in  this  way  are  known  as 
dikes.  They  vary  in  width  from  a  few  inclies  or  even 
a  fraction  of  an  inch  to  hundreds  of  feet,  and  are  fre- 
quently scores  of  miles  in  lengtli.  They  may  appear  as 
vertical  or  variously  inclined  sheets  cutting  across  the 
bedding  of  stratified  or  other  rocks.  In  many  instances, 
molten  rock  has  been  forced  between  stratified  rocks, 
and,  on  cooling,  formed  sheets  having  the  same  bedded 
arrangement  as  the  enclosing  layer.  Layers  of  crystal- 
line rock  orisjinatinoj  in  this  manner  are  termed  intruded 
sheets,  in  distinction  from  surface  overflows,  or  extruded 
sheets.  Under  certain  conditions  not  well  understood, 
molten  rock  forced  into  the  earth's  crust  from  below, 
instead  of  breaking  through  the  strata  or  spreading  out 
between  them,  causes  them  to  rise,  and  cisterns  of  molten 
material  are  formed  beneath  them ;  a  series  of  uplifts 
are  thus  formed,  which  are  known  as  plutonic  plugs, 
laccolites,  and  subtuberant  mountains.^  These  various 
classes  of  igneous  intrusions  occur  in  the  earth's  crust, 
sometimes  at  great  depths,  as  is  shown  hy  the  amount 

1 1.  C.  Russell,  "  Igneous  Intrusions  in  the  Neighborhood  of  the  Black 
Hills,  Dakota,"  "Journal  of  Geology,"  Vol.  4,  pp.  177-194.  "On  the 
Nature  of  Igneous  Intrusions,"  "Journal  of  Geology,"  Vol.  4,  1896,  pp. 
23-43.  "  Igneous  Intrusions  and  Volcanoes,"  "  Popular  Science  Monthly," 
December,  1896. 


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302 


VOLCANOES   OF   NOIITH   AMERICA 


of  rock  oroJcd  away  so  as  to  expose  them  at  the  surface, 
and  must  have  been  forced  m  against  an  enormous  pres- 
sure. The  force  or  pressure  which  caused  these  intru- 
sions is  so  vast  in  many  instances  that  one  fails  to 
compreliend  its  magnitude.  As  described  in  the  papers 
just  referred  to,  great  mountain  ranges  in  the  central 
part  of  North  America  —  like  the  Black  Hills  of  Dakota, 
Big  Horn  Mountain,  Wyoming,  and  the  eastern  range 
of  the  Rockies  in  Colorado  —  belong  to  a  class  of  uplifts 
designated  as  subtuberant  mountains,  and  are  believed 
to  owe  their  origin  to  great  reservoirs  of  molten  rock 
forced  into  the  earth's  crust. 

Relation  between  Igneous  Intrusions  and  Volcanoes.  — 
As  we  have  just  seen,  dikes  result  from  the  filling  of  fis- 
sures with  molten  rock,  which  in  m.ost  instances  is  forced 
in  from  below ;  the  best  explanation  that  has  been  given  of 
the  origin  of  intruded  sheets,  plutonic  plugs,  laccolite,  and 
subtuberant  mountains,  is  that  intruded  rock  was  forced 
upward  through  fissures  in  the  deeper  part  of  the  earth's 
crust  and  expanded  in  various  ways  in  its  more  superficial 
portions,  and  especially  in  regions  of  horizontally  stratified 
beds.  The  primary  conditions  leading  to  the  origin  of 
these  various  forms  of  intrusions,  are :  (1)  deeply  seated 
reservoirs  of  plastic  or  potentially  plastic  rock  in  the  earth's 
crust  or  below"  it,  and  under  great  pressure ;  (2)  fissures 
formed  in  the  crust  and  opening  into  the  deeply  seated 
reservoirs. 

Under  these  conditions  the  highly  heated  material 
below  the  surface,  when  fissures  were  formed  in  the  crust, 
would  become  plastic,  or  perhaps  highly  fluid,  and  being 
under  great  lateral  pressure,  would  be  forced  upward  into 
the  fissures.     The  behavior  of  the  material  injected  into 


)i 


THEORETICAL   CONSIDEIIATIONS 


303 


the  earth's  cnist  in  this  manner  woukl  vary  according  to 
the  character  of  tlie  fissures,  the  deptli  to  which  they 
reached;  tlie  structure  of  the  rocks  through  which  tlie 
magmas  rose,  whether  stratified  or  massive,  and  if  strati- 
fied, whetlier  horizontal  or  inclined,  and  if  water-charged 
or  not ;  the  nature  of  the  magmas  themselves,  whether 
easily  fusible  or  refractory,  etc.  The  influence  of  these 
various  conditions  has  been  considered  in  the  essays 
just  referred  to. 

Volcanoes  in  many  instances  are  known  to  be  located 
on  fissures  in  the  earth's  crust.  The  dissection  of  vol- 
canic mountains  by  erosion  has  shown,  in  many  instances, 
that  the  conduits  through  which  the  lava  rose  were  fract- 
ures, which,  being  filled  with  molten  rock,  formed  dikes  as 
the  magma  cooled. 

It  is  evident,  then,  that  igneous  intrusions  and  volca- 
noes are  phases  of  the  same  process.  Fissures  originat- 
ing in  the  lower  portions  of  the  earth's  crust,  but  failing 
to  reach  the  surface,  would,  on  being  filled  with  molten 
rock,  be  transformed  into  dikes,  and  in  regions  where 
great  thicknesses  of  horizontally  stratified  beds  occur, 
might  lead  to  intruded  sheets,  laccolites,  etc.  If  the  fis- 
sures extended  from  the  highly  heated  interior  to  the  sur- 
face, —  or  if  less  extensive  fissures  are  formed  in  the  lower 
portion  of  the  crust,  and  the  force  of  the  injected  magma, 
acting  like  a  wedge,  prolong  them  to  the  surface,  —  molten 
rock  would  be  poured  out  and  a  surface  overflow  occur, 
that  is,  a  volcano  would  be  formed.  A  single  fissure 
might  thus  lead  to  the  origin  of  intrusions  of  various 
forms,  and  also  to  volcanic  eruptions  of  various  kinds, 
according  to  the  modifying  conditions.  The  primary 
conditions  leading  to  surface  discharges  of   molten  rock 


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VOLCANOES  OP  NORTH   AMEIUCA 


or  extrusions,  arc  the  same  as  those  which  give  origin  to 
suljterranean  injections  or  intrusions. 

Source  of  the  Steam  of  Volcanoes.  — The  most  striking 
feature  of  volcanic  eruptions  and  one,  so  far  as  now  known, 
always  present,  is  the  abundant  escape  of  steam.  Steam 
frequently  escapes  in  vast  quantities  and  even  with  explo- 
sive violence  when  no  molten  rock  is  visible.  The  resem- 
l)lance  of  an  eruption  of  a  mild  cliaracter,  as  when  a 
volcano  is  in  the  Strombolian  stage,  to  the  boiling  of 
mush  in  a  tall  vessel  through  the  actiov.  of  heat  applied 
at  the  bottom,  illustrates  the  action  that  is  witnessed  in 
many  volcanoes.  In  this  explanation  and  in  nio.«t  others 
that  have  been  suggested,  steam  is  appealed  to  as  the 
main  and  essential  force  which  causes  the  molten  lava  to 
rise  in  a  vo!  mic  conduit.  That  steam  given  off  by  vol- 
canoes is  not  the  cause  of  the  rise  of  lava  in  fissures, 
however,  is  indicated  by  the  fact  that  rocks  forming  dikes 
are  not  vesicular,  but,  as  every  geologist  knows,  are  among 
the  most  compact  and  solid  of  igneous  rocks. 

It  has  been  shown  by  Van  Hise,  apparently  on  sound 
principles  and  correct  reasoning,  that  what  may  be  termed 
appreciable  cavities  cannot  exist  in  the  earth's  crust  at  a 
depth  in  excess  of  about  30,000  feet.  This  and  other 
considerations  lead  to  the  conclusion  that  the  portion  of 
the  earth  that  is  water-charged  is  the  outer  layer  of  the 
crust.  Beneath  the  sea  and  land  alike,  except  perhaps 
in  desert  regions,  the  rocks  are  filled  with  water,  prob- 
ably to  the  depth  of  several  thousand  feet.  In  deep 
mines  and  wells,  with  few  exceptions,  the  rocks  are  moist 
and  usually  abundantly  water-charged. 

Molten  magmas,  rising  through  fissures  and  approach- 
ing  the   earth's   surface,  would  invade   a  water-charged 


THKOUETICAL   CON'SIDEIlATIONS 


nor) 


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zone.  The  molten  rock,  on  coming  in  contact  Avith  water 
in  the  rock.s,  would  vaporize  it,  or  even  cause  a  dissocia- 
tion of  its  elements.  It  is  known  that  many  suhstanccs, 
especially  when  heated  and  under  i)ressure,  have  the 
power  of  ahsorbing  gases.  Molten  rock  would,  it  is  be- 
lieved, absorb  the  steam  and  gases  generated  by  coming 
in  contact  with  water,  and  allow  them  to  escape  when 
pressure  is  relieved  or  the  temperature  lowered.  A 
magma  forced  through  the  superlicial  water-charged  layer 
of  the  earth's  crust,  and  reaching  the  surface,  would,  on 
account  principally  of  relief  of  pressure,  give  olf  its  oc- 
cluded steam  and  gases.  If  the  lava  was  highly  liquid, 
this  would  take  place  by  a  boiling  process,  the  steam  and 
gases  escaping  quietly ;  but  if  the  lava  was  viscous,  the 
expansion  of  the  steam  would  be  retarded  until  its  pent- 
up  energy  was  relieved  by  an  explosion.  If  the  molten 
lava  came  in  cortact  with  a  considerable  volume  of  water, 
a  ^'iolent  explosion  would  be  the  inevitaljle  result. 

The  above  considerations  seem  to  indicate  that  steam 
given  off  by  volcanoes  is  derived  from  the  water-charged 
rocks  through  which  the  lava  passes  in  the  upper  portions 
of  their  conduits,  and  also  that  it  is  distinct  in  origin  from 
the  pressure  and  heat  manifested  in  connection  with  it. 

AVhat  is  known  as  dry  fusion,  that  is,  the  melting  of 
substances  from  which  water  is  excluded,  requires  in 
many,  if  not  in  all,  instances  a  much  greater  degree  of 
heat  than  when  water  is  present,  or  what  is  termed  aqueo- 
igneous  fusion.  We  may  reasonably  conclude,  therefore, 
that  a  magma  rising  in  a  fissure  and  entering  the  water- 
charged  portion  of  the  earth's  crust  would  tend  to  be- 
come more  fluid.  At  the  same  time  its  energy  derived 
from  pressure  on  the  reservoir  from  which  it  came  would 


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306 


VOLCANOES   OP   KOKTir    AMKIUCA 


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be  increased  l)y  tliu  cxpansivo  energy  of  the  steam  gen- 
erated. Lava  which  would  not  reach  tlie  surface  by 
reason  of  tiie  pressure  on  its  reservoir,  might,  for  this 
reason,  aetjuirc!  sulli(;ient  energy  to  bring  on  a  surface 
discharge.  Krui)ti()ns  when  water-charged  layers  are 
present  might  thcu'ofore  be  expected  to  bo  more  numer- 
ous than  in  arid  regions.  Tiiis  (juestion  has  S(mie  bearing 
on  the  marked  association  of  volcanoes  with  the  ocean, 
frequently  api)ealed  to  as  showing  that  sea-water  gaining 
access  to  heated  rocks  is  one  of  the  main  causes  of  volcanic 
(eruption,  but  this  matter  will  be  considered  later.' 

The  instance  observed  by  Squire,  cited  on  a  previous 
page  in  connection  with  the  description  of  a  young  vol- 
cano in  Nicaragua,  in  which  an  explosive  eruption 
occurred  in  connection  with  the  first  heavy  rainfall 
that  followed  the  loss  of  energy  after  an  eruption,  is  of 
interest  in  connection  with  the  considerations  just  offered. 
The  effect  of  the  rain  seems  to  have  been  analogous  to 
what  would  happen  if  water  should  be  poured  on  a  bed 
of  highly  heated  furnace-slag ;  that  is,  a  steam  explosion 
occurred. 

There  is  negative  evidence  also  which  tends  to  show 
that  deeply  seated  magmas  are  not  in  the  explosive  condi- 
tion that  frequently  characterizes  volcanic  eruptions.  We 
learn  from  physical  students  that  the  tension  of  water 
vapor  increases  with  increase  of  temperature  at  more 
than  a  simple  ratio.  If  the  earth's  interior  is  vapor- 
charged,  it  must  be  in  a  state  of  vastly  greater  tension 

^I  have  attempted  to  correlate  volcanoes  with  humid  climates,  but 
although  a  large  majority  of  volcanoes  do  occur  in  humid  regions,  yet  as 
the  surface  rocks  are  nearly  everywhere  water-cliarged,  there  does  not  seem 
sufficient  reason  for  concluding  that  this  is  an  important  condition  govern- 
ing their  distribution. 


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THEOIlKTrcAI.  CONSIDKRATroNS 


w: 


than  is  known  from  phy.sH^iil  cxpcrinicnts  or  is  mani- 
fest 1)}'  tliu  most  stu^iondous  volcjinic  (.'X[)I(jsion.  Tlic 
L'f'fuct  of  Wiitcr  in  largo  volumes  on  coming  in  mn- 
tact  Avith  liiglily  li(Jutu(.l  rocks  is  illnstratcfl  hy  the 
eruption  of  Krakatoa,  when  something  lila»  one  culiic 
mile  of  rock  was  blown  to  dust.  If  the  exci'ssivcl}' 
heated  rocks  of  the  earth's  interior  are  steam-chargt'd, 
the  tension  under  which  they  exist  nmst  be  at  least  as 
many  times  greater  than  the  explosive  energy  manifest 
at  Krakatoa  as  the  volume  of  vapor  in  the  earth's  inte- 
rior exceeds  the  volume  of  steam  that  caused  the  explosion 
in  the  Strait  of  Sunda.  1  know  of  no  way  by  which  to 
make  a  (piantitative  measure  of  the  tension  of  the  steam 
in  the  earth's  interior,  inider  this  hypothesis,  but  seem- 
ingly the  comparison  just  made  is  sutficicnt  to  show  that 
under  the  supposition  that  the  steam  given  off  by  vol- 
canoes is  derived  from  the  earth's  interior  and  that  the 
highly  heated  inner  sphere  of  the  earth  is  steam-charged, 
we  would  indeed  be  "living  on  a  volcano."  With  such 
a  vast  volume  of  superheated  steam  within  the  earth,  the 
crust  would  be  at  once  blown  to  fragments.  Besides, 
under  the  generally  accepted  theory  that  the  earth  was 
at  one  time  much  hotter  than  at  present  and  has  cooled 
from  a  molten  condition,  steam,  if  originally  absorbed  by 
the  molten  magma,  must  have  escaped  before  a  crust 
conld  form.  The  consideration  of  wdiat  nmst  follow  in 
case  a  vent  for  the  imprisoned  steam  in  the  earth's 
interior,  vmder  the  supposition  that  the  highly  heated 
interior  is  steam-charged,  was  once  opened,  as  in  the 
formation  of  a  volcano,  is  again  evidence  that  such  vast 
tension  as  the  hypothesis  implies  does  not  exist  within 
the  earth. 


I 


808 


VOLCANOES   or   NORTH   AMERICA 


M. 


i'iijli 


I  vi 


B(jtli  positive  aad  negative  evidence  thus  tend  to  show 
that  volcanic  m..gmas  rising  in  fissures  and  nearing  the 
earth's  surface,  acquire  steam  from  the  water-charged 
rocks  traversed.  As  the  water-charged  portions  of  the 
eartl).  are  superficial,  volcanic  magmas  only  acquire  explo- 
sive energy  on  reaching  the  outer  portions  of  the  crust. 
The  influence  of  various  volumes  of  water  in  the  paths 
of  ascending  magmas,  and  the  character  of  the  explosions 
which  would  accompany  their  coining  together,  remain  to 
be  considered.^ 

Source  of  the  Heat  of  Volcanoes. —  If  the  reader  agrees 
with  me  that  the  source  of  the  steam  given  off  by  vol- 
canoes is  in  the  superficial  portions  of  the  earth's  crust, 
it  will  be  easy  to  understand  that  the  source  of  volcanic 
heat  and  the  source  of  the  force  that  causes  molten  lava 
to  rise  through  fissures  are  distinct  and  should  be  sepa- 
rately considered. 

From  what  is  now  known  concerning  the  progressive 
increase  in  temperature  with  depth  below  the  earth's  sur- 
face, it  follows,  as  has  already  been  assumed,  that  the 
source  of  the  heat  manifested  in  volcanic  eruptions  is  the 
general  internal  heat  of  the  earth.  That  is,  it  is  mainly 
and  essentially  under  the  best  hypotheses  we  have  con- 
cernimi;  the  oriu;in  of  the  earth,  the  residual  heat  of  a 
once  molten  globe. 

Source  of  the  Pressure  which  causes  Molteu  Lava  to  rise 
in  Fissures. —  The  pressure  to  which  the  rocks  composing 
the  earth  are  subjected  increases  with  depth.  Even  in 
the  lower  portion  of  what  is  designated  as   the   earth's 

^  A  concise  disoussion  of  the  causes  of  volcanic  action,  accompanied  by 
many  references  to  original  treatises,  may  be  found,  Prestwich's  "Geology," 
Vol.'l,  ISSG,  pp.  210-210. 


{ i 


\  ^  I 


(    \ 


THEORETICAL  CONSIDEKATIOXS 


309 


crust,  the  pressure  is  so  enormous  that  we  might  easily  ho 
led  to  the  conclusion  that  open  fissures  could  nut  hv 
formed.  The  fact,  ho\v3ver,  that  dikes  occur  in  many 
regions  and  frequently  in  large  numbers,  sho'vs  that  the 
crust  has  been  broken  in  thousands  of  localitic^s,  and  the 
fissures  formed  filled  by  molten  rock  injected  from  below. 
That  the  fissures  thus  filled  were  formed  ijolow  thousands 
of  feet  and  even  tens  of  thousands  of  feet  of  rock  is 
proven  by  their  occurrence  in  regions  that  have  siitfercd 
that  amount  of  erosion. 

In  spite  of  the  natural  conclusion  that  fissures  could 
not  be  formed  in  rocks  under  a  vast  v»'eight  of  super- 
imposed strata,  we  have  the  well-known  fact  that  they 
have  been  formed  in  practically  countless  numljers  in 
such  situations.  An  explanation  of  this  apparent  anomal}' 
is  furnished  by  the  hypothesis  that  the  deeply  seated 
rocks,  on  account  of  their  high  temperature,  are  in  what 
has  been  termed  above  a  potentially  plastic  condition. 
As  soon  as  a  break  is  formed,  pressure  is  relieved ;  the 
rocks  to  which  the  break  penetrates  at  once  l)ec()me 
plastic  and  probably  in  many  instances  highly  fiuid,  and 
on  account  of  pressure  on  all  sides,  except  that  in  wliieh 
movement  is  rendered  possible  by  the  presence  of  the 
fracture,  are  forced  into  the  opening  and  rise  toward  the 
surface. 

Although  deeply  seated  rocks  are  under  such  enormous 
pressure  that  fracture  seems  impossible,  yet  the  potentially 
plastic  rocks  to  which  the  deeper  fractures  penetrate  Jire 
luider  a  pressure  of  an  equal  order  of  magnitude.  As 
pressure  increases  witli  depth,  the  pressure  on  the  deeply 
seated  and  potentially  plastic  rocks  are  sul)jected  to 
greater  lateral  pressure  than  that  which  tends  to  close  the 


;(  •     ! 


I 

X 


■'(11 


iHnwyigi 


\ 


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1      i 


'li  I  ) 


1(1 


1  . 

1" 

,t 

'if 

'l, 

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1 

,  1 

•  fl 

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!) 

i 

4 

1 

I 


il 


f 


Hi 


I    Li- 


J! 


310 


VOLCANOES    OF   NORTH    AMERICA 


breaks  fonned  in  tho  rocks  above  them.  If  these  prem- 
ises are  correct.  —  and  there  seems  to  be  no  way  of 
escaping  the  cunchisions  reached,  —  the  result  would  be 
that  the  highly  boated  rocks  reached  by  a  fissure  would 
at  once  become  plastic  and  would  be  forced  into  the  break, 
and  would  tend  to  press  its  walls  wider  apart.  Tl;e  ex- 
tent to  whicli  a  magma  would  rise  in  a  fissure  n-ould 
depend  on  several  considerations ;  chief  among  whicli 
would  be  the  pressure  on  the  reservoir  from  whicli  it 
came,  and  the  resistance  it  encountered  as  it  rose.  The 
pressure  would  be  determined  by  the  depth  of  the  reser- 
voir. The  resistance  met  with  as  the  magma  was  forced 
upward  would  be  regulated  by  the  size  of  the  break,  its 
regularity,  temperature  of  the  magna,  lateral  pressure 
tending  to  close  the  break,  etc.  All  of  the  retarding  in- 
fluences, excejjt  perhaps  the  last,  may  be  designated  by 
the  term  friction.  There  would  be  friction  against  the 
sides  of  the  fissure,  and  internal  friction  in  the  magma 
itself,  each  of  which  would  depend  largely  on  temperature. 
As  the  temperature  decreased  by  conduction,  etc.,  the 
magma  would  1)ecome  less  and  less  plastic,  the  friction  of 
flow  would  increase,  and,  finally,  when  solidification  en- 
sued, the  motion  would  cease.  For  these  reasons,  a 
mao-ma  entering  a  larare  fissure  would  tend  to  rise  higher 
than  in  a  narrow  fissure.  Dikes  deep  wnthin  the  earth's 
crust  should,  therefore,  be  more  numerous  than  in  its 
surface  portion. 

The  study  of  fractures  and  faults  in  the  earth's  crust 
has  shown  that  such  breaks  are  seldom  due  to  continuous 
smooth-sided  fractures,  but  are  rather  splintering  breaks, 
which  overlap  and  cross  one  another,  with  many  off- 
shoots.   They  are  more  often  belts  of  intersecting  fractures 


r 


\ 


.'.»..JWLV  .''. 


^wiiii'~«  H»jrT3.i 


THEORETICAL   CONSIDERATIONS 


811 


\  ( I 


\-u 


than  single  clean-cut  gashes.  A  magma  rising  in  such  a 
belt  of  fracture  would  h?ve  to  force  its  way  from  one 
break  to  another,  and  would  send  oft'  many  branches.  I 
think  that  all  geologists  will  admit  tiiat  these  considera- 
tions agree  with  what  is  found  when  dikes  are  studied. 

From  what  has  just  been  stated,  it  follows  that  the 
resistance  to  be  overcome  as  a  magma  rises  toward  the 
surface  becomes  greater  and  greater ;  as  will  be  shown 
later,  compensation  for  this  progressive  increase  in  resist- 
ance is  found  when  the  water-charged  portion  of  the 
earth's  crust  is  reached  and  steam  is  generated. 

The  considerations  just  offered,  I  trust,  will  make  it 
clear  that  the  siource  of  the  heat  manifested  in  volcanoes, 
and  the  source  of  the  pressure  which  causes  a  magma  to 
rise  in  a  fissure,  are  distinct ;  and  that  the  force  tending 
to  inject  a  magma  into  a  fissure  is  the  pressure  of  the 
earth's  crust  on  the  potentially  plastic  reservoir  from 
which  it  flows. 

Differences  in  Volcanic  Lavas. — Objections  have  been 
made  to  the  hypothesis  that  volcanoes  derive  their  lava 
from  the  highly  heated  interior  of  the  earth,  on  the 
ground  that  different  volcanoes  erupt  lava  of  different 
composition,  and  that  changes  occur  in  the  composition  of 
the  lava  extruded  at  different  times  from  the  same  vent. 

These  oljjections  were  valid  so  long  as  the  interior  of  the 
earth  was  thought  to  be  in  a  molten  condition.  If,  liow- 
ever,  we  consider  tliat  the  earth  beneath  the  cold,  outer 
shell  is  solid  by  reason  of  pressure,  but  becomes  plastic 
as  so(jn  as  pressure  is  relieved,  the  ditticulty  disappears. 
The  highly  heated  interior  is  evidently  not  homogeneous, 
as  is  shown  by  the  products  of  volcanoes,  and  as  is  known 
also  from  pendulum  observations. 


M 


1*;.  : 


1  H' 


7 


1 1 


i«M 


II       ( 


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f 

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1, 

H 


1    ' 

1 

j 

1 

ik 

■•    J 
tiki.  ■-1 

312 


VOLCANOES   OF   NORTH   AMERICA 


Under  the  hypothesis  here  advanced,  a  local  relief  of 
pressure,  due  to  the  opening  of  a  fissure  in  the  cooled 
crust,  would  be  followed  at  once  by  a  local  change  of  the 
highly  heated  rocks  penetrated,  to  a  plastic  or  fluid  con- 
dition. The  nature  of  the  magma  rising  in  such  a  break 
would  depend  on  the  composition  of  the  heated  rocks 
reached,  and  from  what  we  know  of  the  com})osition  of 
both  plutonic  and  volcanic  rocks,  evidently  differs  with 
both  lateral  and  vertical  distribution. 

The  reason  for  variations  in  the  composition  of  the 
earth's  interior  is  beyond  our  present  knowledge,  unless 
perhaps,  as  may  be  suggested  under  the  meteoric  hypothe- 
sis, the  earth  has  been  formed  by  the  coming  together  of 
meteoric  bodies  of  various  composition.  It  is  known  that 
portions  of  the  earth's  crust  have  been  weighted  by  sedi- 
mentation and  depressed,  so  that  matter  formerly  at  the 
surface  has  passed  to  the  highly  heated  interior.  Such 
transfers  of  portions  of  the  crust  to  the  interior  would 
produce  heterogeneity  in  the  subcrustal  portion,  and  in 
the  very  regicju,  as  will  be  shown  later,  where  volcanoes 
most  frequently  occur,  that  is,  on  the  borders  of  con- 
tinental areas. 

Independence  of  Neighboring  Volcanoes.  — Another  objec- 
tion urged  with  consistency  against  the  supposition  that 
the  earth's  interior  is  in  a  liquid  condition,  is  that  neighbor- 
ing volcanoes  frequently  erupt  independently  and  without 
sympathy  one  with  another.  A  lofty  volcano  is  sometimes 
in  activity,  while  a  much  lower  but  still  active  neighboring 
crater  is  quiescent.  Under  the  hypothesis  here  advanced, 
this  objection  disappears.  If  the  earth's  interior  is  solid, 
but  in  a  potentially  plastic  condition,  and  branching  and 
irregular  fractures  are  opened  from  time  to  time  in  the 


THEOUETICAL  CONSIDERATIONS 


313 


crust  through  which  magmas  are  forced  out,  it  is  evident 
that  neighboring  fractures  may  be  independent  of  each 
other,  and  also  that  branches  of  a  main  fracture  may 
become  closed  and  opened  independently. 

Origin  of  Fractures  in  the  Earth's  Crust.  — In  reference 
to  the  general  cause  which  produces  fractures  in  the  earth's 
crust,  an  appeal  is  commonly  made  to  the  effect  of  the 
shrinking  of  the  earth  on  cooling,  and  the  folding  and 
breaking  of  the  rigid  crust  in  order  to  conform  with  the 
shrinking  interior.  Beyond  this  general  explanation  it  is 
not  practicable  to  go  in  this  elementary  treatise. 

Under  the  hypothesis  of  a  cooling  globe  it  may  be  sur- 
mised that  while  the  crust  was  thin,  folding  would  go  on 
more  easily  than  when  a  greater  thickness  was  reached ;  and 
that  as  greater  rigidity  was  attained,  fractures  would  become 
more  common.  As  the  crust  thickened,  also,  its  weight 
would  Ijccome  greater,  and  hence  the  pressure  on  the  still 
highly  heated  interior  augmented.  The  conditions  leading 
to  the  formation  of  volcanoes  should,  therefore,  increase, 
at  least  for  a  time,  as  the  earth  cooled,  but  as  the  crust 
became  thicker  and  more  and  more  rigid,  the  conditif»ns 
favoring;  the  extrusion  of  lava  at  the  surface  would  be  ex- 
pected  to  decrease  and  finallj^  cease.  With  a  thin  crust 
and  comparatively  small  pressure  on  the  highly  heated  in- 
terior, an  adjustment  of  the  crust  to  the  shrinking  interior 
would  be  secured  by  a  moderate  extrusion  of  lava  from 
many  breaks;  but  as  the  crust  increased  in  thickness, 
greater  eruptions  from  a  decreased  number  of  fractures 
might  be  expected. 

The  geological  history  of  the  earth  seems  to  be  in 
harmony  with  these  general  considerations,  since,  in  North 
America  at  least,  there  is  comparatively  little  evidence  of 


:(';' 


o 


If 


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1 


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r 

ij, 

,i'    1 

1;:    1 

:    1  I 

—  ., — *.«■ 


'  i\ 


'i 


m-i' 


■I 


814 


VOLCANOES   OF   NOIITH    AMERICA 


volcanic  action  previous  to  the  Jura-Trias.  The  great 
volcanoes,  not  only  of  this  continent  but  of  the  world, 
belong  to  Tertiary  and  more  modern  times.  This  is  not 
because  ero.sion  has  removed  the  more  ancient  volcanoes, 
as  is  shown  by  the  fact  that  "  basal  wrecks "  of  vol- 
canoes of  older  date  than  the  Mesozoic  are  rare.  This 
is  perhaps  unsound  reasoning,  since  many  "  basal  wrecks  " 
must  be  buried  beneath  later  sediments.  Geological  evi- 
dence seems  to  show,  however,  that  volcanic  activity  in- 
creased with  geological  ages,  and  reached  its  maximum 
in  Tertiary  times.  This  same  line  of  reasoning  leads  us 
to  expect  fewer  volcanoes  in  the  future,  owing  to  the  con- 
stantly increasing  resistance  to  the  passage  of  magmas 
from  the  interior  to  the  surface  through  the  thickening 
crust,  but  fissures  once  opened  should  give  origin  to  vol- 
canic phenomena  on  a  grand  scale.  A  decrease  in  the 
number  of  volcanoes  should  be  accompanied  for  a  time 
by  an  increase  in  size,  but  when  the  crust  attained  a  great 
thickness  all  surface  manifestations  of  the  internal  heat 
should  cease  even  Ijefore  the  condition  of  a  completely 
cooled  globe  is  reached. 

Association  of  Volcanoes  with  the  Sea.  —  As  has  fre- 
quently been  pointed  out,  volcanoes,  with  but  few  excep- 
tions, are  situated  on  the  sea  floor  or  on  islands  and  along 
the  borders  of  continents.  This  has  been  assumed  as  evi- 
dence that  the  presence  of  sea-water,  or  perhaps  more 
properly  of  a  body  of  surface  water  whether  connected 
with  the  sea  or  not,  is  one  of  the  conditions  controlling 
the  origin  of  volcanoes ;  the  hypothesis,  still  current  to 
some  extent,  being  that  sea-water  gains  access  to  the 
highly  heated  rocks  of  the  earth's  interior  either  through 
fractures  or  by  percolation,  and  leads  to  the  generation  of 


m  m 


mmsm 


p^ 


"Wt 


TIIEOUETICAL   CONSIDERATIONS 


315 


of 


steam,  which  is  followed  by  eruptions  at  the  surface.  The 
idea  of  a  deeply  seated  origin  for  volcanic  rocks,  and  the 
independence  of  the  sources  of  the  heat  and  pressure,  do 
not  enter  into  this  hypothesis. 

In  support  of  the  hypothesis  that  volcanoes  are  initiated 
by  the  access  of  sea-water  to  the  highly  heated  rocks  1)0- 
neath  the  crust,  it  has  been  pointed  out  by  various  geolo- 
gists, that  the  gases  evolved  from  volcanoes  are  frequently 
such  as  might  l^e  produced  by  the  decomposition  of  sea- 
water.  It  has  been  shown,  notably  in  the  case  of  Vesu- 
vius, that  the  country  about  a  volcano  after  an  eruption  is 
sometimes  whitened  over  large  areas  with  common  salt. 
The  force  of  this  argument,  however,  is  weakened  when  we 
remember  that  volcanic  conduits  frequently  pass  through 
great  thicknesses  of  stratified  rocks,  which  are  sea  sedi- 
ments and  were  changed  at  the  time  of  their  deposition 
with  saline  water.  Many  portions  of  the  outer  layers  of 
the  earth  are  known  to  be  saturated  with  sea-water ;  and 
m  several  regions,  some  of  them  of  broad  extent,  there 
are  beds  of  rock  salt.  Evidently,  then,  volcanoes  might 
erupt  substances  like  those  contained  in  sea-water,  or 
gases  formed  by  their  decomposition,  without  any  direct 
connection  with  the  sea. 

The  origin  of  the  steam  of  volcanoes,  as  has  been  shown, 
can  be  accounted  for  by  the  passage  of  molten  lava  through 
water-charged  rocks.  It  has  been  pointed  out  that  the 
rocks  beneath  land  areas  are  generally  water-charged  from 
surface  precipitation.  These  considerations,  it  seems  to 
me,  remove  all  support  from  the  hypothesis  that  volcanoes 
have  a  necessary  conne>,tion  with  surface  water-bodies. 
The  fact  still  remains,  however,  that  volcanoes  occur  prin- 
cipally on  the  borders  of  continents. 


I " 


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816 


VOLCANOES   OF  NORTH   AMERICA 


Several  geologists  htavo  stiuliefl  the  distribution  of 
oceans  and  continents  and  sought  to  explain  their  ori- 
gin. It  is  known  that  these  greater  features  of  the 
earth's  surface  have  been  somewhat  well  defined  for 
geological  ages.  In  fact,  the  continents  and  oceans 
were  outlived  l)efore  the  appearance  of  the  first  known 
fauna  on  tlie  earth.  Dana  has  sought  to  explain  the 
origin  of  continents  by  saying  that  their  borders  were 
"  original  lines  of  weakness "  in  the  earth's  crust,  and 
that  movements  along  these  lines,  or  more  properly, 
belts,  have  been  continued  to  the  present  day.  What 
determined  the  original  lines  of  weakness  remains  un- 
explained. The  questions  that  here  present  themselves 
are  too  wide-reaching  to  be  discussed  at  this  time,  even 
if  I  had  the  ability  to  do  them  justice ;  but  enough  seems 
clear  to  explain  the  distribution  of  volcanoes,  and  to 
show  that  they  have  no  direct  and  causal  relation  to 
existing  water-bodies.  The  borders  of  continents,  as  is 
well  known  and,  I  think,  universally  conceded  by  geolo- 
gists, are  belts  along  which  repeated  movements  have 
taken  place.  They  are  belts  along  which  the  folding 
and  fracturing  of  the  earth's  crust  have  been  most  fre- 
quent. Being  belts  in  which  fractures  have  occurred, 
they  are  the  regions  where  molten  rock  forced  through 
the  fractures  has  given  origin  to  volcanoes.  The  pres- 
ence of  volcanoes  on  the  borders  of  continents  is,  then, 
the  result  of  some  antecedent  condition,  which  estab- 
lished belts  of  weakness  in  the  earth's  crust.  Along 
these  belts,  movements  have  taken  place  on  account  of 
the  earth's  shrinking  on  cooling,  and  also  by  reason  of  the 
shifting  of  material  on  the  earth's  surface,  and  possibly 
other  causes. 


i  H 


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THEORETICAL  CONSIDERATIONS 


817 


There  are  lines  of  fracture  remote  from  the  sea,  —  as 
in  the  Great  Basin  region,  to  the  east  of  tlie  Sierra 
Nevada,  —  and  in  sucli  regions  volcanoes  occur  hundreds 
of  miles  inland.  The  only  logical  conclusion  in  refurence 
U)  the  distribution  of  volcanoes,  which  seems  at  all  ten- 
able, is  that  they  occur  where  fractures  have  been  made 
in  the  earth's  crust,  and  that  they  are  not  necessarily 
dependent  on  the  distrilnition  of  land  and  water  on  the 
earth's  surface  The  association  of  volcanoes  with  tlie 
Ijorders  of  continents  nuist,  tliurefore,  be  considered  as  of 
the  nature  of  a  coincidence,  the  boundaries  of  continents 
and  the  distribution  of  volcanoes  having  been  determined 
])}•  a  common  cause. 

Influence  of  Water  on  Volcanic  Eruptions.  —  Although 
there  does  not  seem  to  be  a  genetic  relationship  between 
volcanoes  and  surface  waters,  yet  water  dues  play  an 
important  part  in  determining  the  nature  of  volcanic 
eruptions  and  even  in  producing  discharges  of  molten 
rock. 

If  we  imagine  a  fissure  formed  in  dry  rocks,  and  a 
molten  magma  forced  through  it  to  the  surface,  the 
result  would  be  an  overflow  of  lava.  If  the  lava  is  in 
a  condition  of  "dry  fusion,"  —  that  is,  fusion  without 
water  above  that  chemically  combined,  —  the  outflow 
at  the  surface  would  be  similar  to  what  occurs  when 
molten  slag  is  drawn  off  from  a  furnace.  The  eruptions 
would  be  of  the  quiet  type,  and  not  accompanied  Ijy 
explosions.  Under  these  conditions,  the  lava  nmst  lose 
more  and  more  heat  the  higher  it  rises  in  the  earth's 
crust,  and  consequently  becomes  less  and  less  plastic. 
In  many  instances,  it  may  be  imagined  the  lava  would 
rise  near  to  the  surface,  but  be  checked  in  its  ascent  by 


\ 


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818 


VOLCANOES    OK    NOltTH    AMKUIf'A 


:#f  ■ 


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l)econiing  too  rigid  to  be  forcuil  out.  The  friction  of 
flow  would  increase  in  an  inverse  ratio  to  the  plasticity 
of  the  magma.  If,  however,  this  stage  is  reached  in 
water-chai'ged  rocks,  steam  will  be  generated  and  ab- 
sorbed, the  highly  heated  lava  will  become  more  fusible 
on  account  of  the  pressure  of  occluded  steam,  and  there- 
fore capable  of  being  forced  out  by  a  pressure  that  it 
would  successfully  resist  if  it  had  not  come  in  contact 
with  water.  Viscous  lava,  also,  on  coming  in  contact 
with  large  bodies  of  water  in  the  earth's  crust,  might 
generate  sufficient  steam  to  blow  out  a  passageway  to 
the  surface. 

Even  from  this  brief  statement,  it  will  be  seen  that 
water  in  the  superficial  portion  of  the  earth's  crust  has 
an  important  influence  not  only  in  varying  the  character 
of  volcanic  eruptions,  but  of  inducing  surface  discharges 
in  cases  where  the  pressure  from  beneath  fails  to  force 
a  magma  to  the  surface.  Force  is  added  to  the  upper 
portion  of  a  lava  column  which  is  not  present  before  it 
enters  the  water-charged  rocks.  This  force  —  the  tension 
of  steam  —  is  added  to  the  force  derived  from  pressure 
deep  below  the  surface,  and  is  accountable  for  many  (jf 
the  phenomena  attending  eruptions.  The  importance  of 
this  added  force  is  so  great  that  it  has  been  mistaken  for 
the  primal  cause  of  volcanic  extrusions. 

In  brief :  during  volcanic  eruptions,  there  is  a  rise  of 
molten  or  plastic  rock  through  fissures,  and  a  descent 
of  surface  water  through  fissures  and  by  percolation ;  the 
meeting-place  of  these  two  important  elements  is  in  the 
superficial  portion  of  the  earth's  crust.  The  maximum 
depth  to  which  surface  water  penetrates  is  probably  not 
over  30,000  feet,  and,  in  general,  the  quantity  of  water 


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TII K( )UETI(' A L   C( >NSI I )EU ATKINS 


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I        J 


present  in  a  given  volume  oi  rock  increases  from  near 
that  (le})tli  to  tlie  snrfaee.  In  addition  to  water  [M-rcolat- 
ing  downwaril,  there  is  water  in  the  case  of  si'dlmentary 
layers  wliich  Avas  retained  by  them  at  tiie  time  of  their 
deposition . 

Other  Hypotheses 

The  exphmaticms  offered  in  tlie  preceding  [)ortions  of 
this  oliapter,  in  reference  to  tiie  nature  and  origin  of 
volcanic  eruption,  differ  from  most  of  tiie  previously 
entertained  hypotheses  that  have  heen  advanced  to  ac- 
count for  volcanic  phenomena;  and,  in  justice  to  the 
stndent  who  obtains  his  first  introduction  to  volcanoes 
from  these  pages,  it  is  proper  that  at  least  sonu; 
account  of  explanations  previously  offered  should  be 
given.  Space  will  not  permit  more  than  a  glance  into 
this  branch  of  the  subject,  but,  from  the  references 
given,  the  reader  will  be  enabled  to  compare  hy[)otheses 
for  hliiiself  and  be  led  to  independent  conclusions.* 

Chemical  Hypothesis.  —  In  an  early  stage  in  the  study 
of  volcanoes  it  was  suggested  that  the  interior  of  the 
earth  consists  of  unoxidized  alkaline  metals,  and  that  the 
penetration  of  water  caused  oxidation  to  take  place  with 
the  production  of  great  heat.  This  hypothesis,  although 
advocated  by  Davy  and  Danbeny,  was  linally  abandoned 
by  the  former,  and  now  is  of  historic  interest  simply. 
The    products   of   volcanoes   show   that   conditic^ns    even 

^  Discussions  of  various  lij'potlieses  advanced  to  account  for  volcanic 
phenomena  may  he  found  in  the  following  books:  G.  I*.  Scrope,  "Con- 
siderations of  Volcanoes,"  London,  ISJ").  J.  W.  Judd,  "  Volcanoes," 
New  York,  1881,  pp.  3;n-3G!).  Joseph  Piestwich,  "Ceoloov,"  Vol.  I,  ISSH, 
j>p.  210-216.  Joseph  Prestwich,  "On  the  Agency  of  Water  in  Volcanic 
Eruptions,"  in  Royal  Society  of  London,  Proceedings,  Vol.  41,  1880,  pp. 
117-173. 


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23  WiST  MAIN  STRSET 

WEBSTER,  N.Y.  UStO 

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320 


VOLCANOES   OF   NOllTH   AMERICA 


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remotely  similar  to  those  postulated  do  not  exist  in  the 
regions  from  which  volcanic  rocks  are  derived. 

Mechanical  Hypothesis.  —  It  has  been  suggested  by 
Mallet  ^  that  when  movements  in  the  earth's  crust  occur, 
as  when  rocks  are  folded  or  faulted,  the  fricl.ion  is  such 
that  sufficient  heat  is  produced  to  fuse  rocks  and  bring  on 
volcanic  conditions. 

The  movements  of  rocks  referred  to  unquestionably 
result  in  the  conversion  of  some  of  the  energy  expended 
into  heat.  Such  earth  movements,  however,  are  believed 
in  most  instances  to  progress  slowly,  so  that  the  heat  pro- 
duced is  diffused  by  conduction,  etc.,  and  a  temperature 
necessary  to  fuse  rocks  would  not  be  expected  to  be 
reached  in  most  instances.  Besides,  in  many  regions,  as 
for  example  in  the  Appalachians,  there  has  been  intense 
folding  and  much  faulting,  but  volcanoes  are  absent.  The 
walls  of  great  faults  and  the  surfaces  brought  in  contact 
by  overthrusts  do  not,  so  far  as  observed,  exhibit  evidence 
of  fusion  having  occurred.  Recent  theories  concerning 
the  metamorphism  of  rocks  ascribe  profound  changes  in 
mineralogical  and  chemical  composition  to  the  effects  of 
dynamical  changes,  which  certainly  favors  the  views  ex- 
pressed hy  Mallet.  On  the  whole,  however,  the  mechanical 
hypothesis  has  not  been  generally  accepted  by  geologists, 
and  does  not  seem  to  adequately  explain  many  of  the  phe- 
nomena associated  especially  with  intruded  rocks,  which, 
so  far  as  their  genesis  is  concerned,  must  be  studied  in 
connection  with  surface  extrusions. 

Steam  Hypotheses.  —  The  consideration  that  steam  is 
the   main   propelling   force   which   causes   lavas   to   rise 

1 "  On  Volcjiuic  Energy,"  Philosophical  Transactions  of  the  Royal  Society, 
1873,  p.  M7. 


^mm^mm 


i^ 


THEOKETICAL  CONSIDEUATIONS 


321 


through  fissures  in  tlie  oartli's  crust,  lias  ah'eiidy  been  re- 
ferred to,  and  several  objections  to  it  suggested.  Hypothe- 
ses based  on  the  idea  that  steam,  which  plays  sucli  an 
important  part  in  many  eruptions,  is  in  reality  the  main 
cause  of  the  rise  of  lava  from  deep  within  the  earth,  have 
been  advanced  with  various  modilications  by  Scrope,' 
Lyell,^  Judd,""^  Reade,'*  and  others. 

Objections  to  the  hypothesis  thai  steam  is  the  main 
source  of  the  energy  which  brings  about  volciinic  erup- 
tions, have  been  formulated  by  Prestwich,  and  still  remain 
mianswered.  In  addition  to  the  considerations  referred 
to,  others  might  be  enumerated  in  reference  to  the  nature 
and  origin  of  intruded  igneous  rocks,  for  the  reason,  as 
already  urged,  that  intruded  and  extruded  rocks  result 
from  variations  in  a  single  process.  The  criticisms  on 
what  I  have  termed  the  "  steam  hypotheses  "  by  Prest- 
wich ^  are  as  follows : 

"(1)  If  the  molten  mass  were  so  permeated  by  gases 
and  vapors,  the  eruption  of  lava  and  the  discharge  of 
vapors  would  always  be  concurrent,  and  there  could  be  no 
discharge  of  the  one  without  the  accompaniment  of  the 
other ;  whereas  there  are  many  eruptions  which  are  al- 
together explosive,  while  in  other  eruptions  —  many  of 
them  very  large  —  the  flow  of  lava  is  effected  quietly  and 
without  the  detonations  and  ejections  caused  by  the  explo- 
sion of  vapors.  (2)  Another  objection  is  that  all  lavas 
would   be   more   uniformly  scoriaceous,  and   that    vapor 

1 "  Considerations  on  Volcanoes,"  London,  1825,  pp.  17,  66. 
2  «  Principles  of  Geology,"  tenth  edition.  Vol.  II,  p.  221. 
8 "  Volcanoes :  what  they  are   and  what  they  teach,"  New  York,  1881, 
pp.  33,  30,  331-369. 

* "  The  Origin  of  Mountain  Ranges,"  London,  1880,  pp.  253-265. 
6 Joseph  Prestwich,  -'Geology,"  Vol.  T,  1886,  pp.  212,  213. 


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322 


VOLCANOES   OF   NOKTH   AMEUICA 


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bubbles  would  show  themselves  more  generally  ;  but  there 
are  lavas  which  are  perfectly  compact,  although  they 
have  outflowed  under  the  usual  atmospheric  pressure, 
(o)  Again,  it  is  difficult  to  conceive  how  these  vapors  and 
g'lses  could  have  become  incorporated  with  the  molten 
magma,  unless  we  admit,  with  Dr.  Sterry  Hunt,  that  be- 
tween the  solid  crust  and  the  solid  nucleus  of  the  earth, 
there  is  a  layer  consisting  of  the  outer  part  of  the  'origi- 
nally congealed  mass,  disintegrated  and  modified  by 
chemical  and  primitive  mechanical  agencies  and  impreg- 
nated with  water,  now  in  a  state  of  igneo-aqueous  fusion ; 
or  with  Mr.  Osmond  Fisher,  who  connects  volcanic  erup- 
tions with  the  extravasation  of  a  primogenial  water-sub- 
stance in  the  molten  magma.  Otherwise,  that  water 
could  find  its  way  down  to  the  volcanic  foci  through  the 
crust  of  the  earth  is  highly  improljable,  as  a  point  must 
be  reached  where  there  is  reason  to  suppose  the  tension 
of  the  vapor  will  equal  the  hydrostatic  pressure  of  the 
descending  water  and  stay  its  course.  Further,  if  such 
were  not  the  case,  not  only  the  volcanic,  but  likewise  the 
plutonic,  rocks  would  have  been  subjected  to  ejection 
under  the  same  conditions  and  with  similar  subaerial 
results. 

"  Another  hypothesis,  which  also  assumes  water  to  be 
the  prime  motor  of  eruption,  but  considers  its  introduction 
to  the  volcanic  foci  to  be  coincident  with  the  eruption 
itself,  supposes  fissures  to  be  formed  in  the  bed  of  the  sea, 
by  which  a  direct  passage  is  opened  for  the  sea-water. 
The  objections  to  this  hypothesis  are,  that  it  is  not 
possible  to  suppose  a  fissure  down  which  water  could 
have  passed  without  its  forming  a  passage  for  the  escape 
of  the  lava  itself;  nor  can  we  conceive  the  steam,  if  so 


THEOKETICAL   CONSIUEllATIOXS 


328 


•^y 


be 


produced,  could  have  had  the  force  to  eject  a  column  of 
Liva  of  the  height  required  to  reach  froui  the  volcanic 
foci  to  the  summit  of  the  volcano,  or  that  it  would  take 
the  longer,  more  resisting,  and  more  indirect  channel  in 
presence  ol  the  open  and  unobstructed  fissure." 

An  exhaustive  discussion  of  all  the  various  hypotheses 
that  have  been  advanced  to  account  for  volcanic  phe- 
nomena, is  impracticable  at  this  time,  but  this  chapter 
would  be  markedly  incomplete  without  a  reference  to  a 
modification  of  the  steam  hypothesis  recently  proposed  by 
Shaler.'  The  essential  features  of  the  hypothesis  re- 
ferred to  are  that  oceanic  sediments  of  which  most  strati- 
fied rocks  are  composed,  are  charged  at  the  time  of  their 
deposition  with  sea- water,  and  may  attain  great  thick- 
ness. As  layer  on  layer  of  strata  are  laid  down,  the  base- 
ment portion  of  the  pile  becomes  heated  by  conduction 
from  the  earth's  interior;  the  successive  layers  acting 
like  blankets  in  retarding  the  escape  of  the  heat  of  the 
earth.  As  stated  by  Shaler :  "  We  thus  see  that  in  the 
water  imprisoned  in  the  deposits  of  the  early  geological 
ages  and  brought  to  a  high  temperature  by  the  blanketing 
action  of  the  more  recently  deposited  beds,  we  have  a 
sufficient  cause  for  the  great  generation  of  steam  at  high 
temperatures,  and  this  is  the  sole  essential  phenomenon  of 
volcanic  eruptions.  "We  see  also  by  this  hypothesis  why 
volcanoes  do  not  occur  at  points  remote  from  the  sea,  and 
why  they  cease  to  be  active  soon  after  the  sea  leaves  their 
neig;hborhood.   .   .   . 

"  The  foregoing  considerations  make  it  tolerably  clear 
that  volcanoes  are  fed  from  deposits  of  water  contained 

1 X.  S.  Shaler  "Aspects  of  the  Earth,"  Xew  York,  1889,  pp.  46-97.  Also, 
"Scribner's  Magazine,"  February,  1888. 


f 


TlfilW^PI 


3-24 


VOLCANOES    OF    NOKTH    AMKItICA 


i       'i 


in  iincioiit  rock.s  whi(.^li  liavu  bocoino  greatly  heated 
tlirouuli  tlie  blanket iiiL!;  ei'fects  of  the  strata  which  have 
been  laid  down  upon  them.  The  gas  which  is  the  only 
hi  variable  element  of  volcanic  eruptions  is  steam  ;  more- 
over, it  is  the  steam  of  sea-water,  as  is  proven  by  analysis 
of  the  ejections.  It  l)reaks  its  way  to  the  surface  only  on 
those  parts  of  the  earth  whicih  are  near  to  where  the 
deposition  of  strata  is  lifting  the  tem[)erature  of  water 
contained  in  rocks  by  preventing,  in  fact,  the  escape  of 
the  earth's  heat." 

In  answering  probable  objections  to  this  hypothesis,  its 
author  states  that  the  only  seriou?:  question  arises  in  ref- 
erence to  the  thickness  of  the  rocks  which  have  been  laid 
down  on  the  sea  floor.  In  this  connection  it  is  remarked: 
"  Hardly  any  geologist  will  doubt  that  it  is  entirely 
within  bounds  to  assume  that  thickness  to  exceed  twenty 
miles.  It  may  well  have  attained  twice  or  thrice  that 
depth  since  the  geological  ages  began." 

In  reference  to  the  statements  made  in  the  last  quota- 
tion, it  must  be  acknowledged  that  the  thicknesses  of 
stratified  rocks  assumed  are  purely  a  matter  of  opinion; 
no  such  thickness  of  stratified  beds  in  one  pile  has 
ever  been  observed.  Instead  of  subscribing  to  the  state- 
ment that  geologists  are  practically  agreed  as  to  the  vast 
thickness  of  stratified  beds,  I,  for  one,  must  dissent  from 
such  a  conclusion  until  proof  is  advanced  to  sustain  it. 
Whatever  the  aggregate  thickness  of  sedimentary  beds 
deposited  during  various  geological  ages  may  be,  the 
essential  part  of  the  hypothesis  is  that  the  sedimentary 
beds  should  be  immensely  thick  in  a  given  locality. 

Marine  sedimentation  usually  continues  only  so  long 
as  subsidence  carries  the  added  material  below  sea  level. 


m 

pi 


THEOKKTICAL   CONSIDEnATrOXS 


325 


An  increase  in  the  thickness  of  sedinientary  hcds  will 
cause  a  rise  of  temperature  in  tlieir  l)asal  portions  espe- 
cially, as  claimed  hy  Shaler,  hut  this  means  an  increase 
in  volume,  and,  as  [)ointed  out  hy  Ueade  and  others,  an 
elevaticm  of  the  surface.  It  appears,  therefore,  in  locali- 
ties where  thick  sediments  accunudate,  that  an  excessive 
thickening  should  he  checked,  if  for  no  other  reason,  by 
elevation  due  to  rock  expansion,  which  -would  carrv  the 
surface  ahove  sea  Ic'vid,  and  such  excessive.'  thicknesses  of 
stratified  beds,  as  is  essential  to  the  liypothesis  referred  to, 
C(juld  not  he  expected  to  occur. 

One  of  the  deepest  sections  of  stratified  rocks,  consist- 
ing largely  of  Paleozoic  sediments,  yet  measured  in 
America,  occurs  in  the  middle  Ap})alachiau  region,  but 
volcanoes  and  volcanic  rocks  of  post-Paleozoic  date  are 
absent.  The  thickness  found  is  not  enough,  to  be  sure,  to 
meet  the  requirements  of  this  hypothesis,  but  it  apjjcars 
to  be  one  of  the  best  test  cases  that  can  be  sun-wsted. 

The  claim  made  in  the  liypothesis  under  considera- 
tion—  that  steam  is  the  sole  essential  phenomenon  of 
volcanic  eruptions  —  has  been  considered  on  previous 
pages,  where  the  evidence  of  the  independent  origin  of  the 
pressure,  heat,  and  steam  manifest  in  volcanoes  has  been 
presented.  If  the  reasons  for  considering  the  essential 
independence  of  these  chief  causes  for  volcanic  phenomena 
are  valid,  it  is  evident  that  to  account  for  tlie  escape  of 
steam  during  a  volcanic  eruption  will  not  furnish  a  com- 
plete theory  of  the  origin  of  volcanoes. 

The  student  will  find  on  reading  Shaler's  very  interest- 
ing and  suggestive  paper,  that  the  essential  connection 
between  volcanoes  and  subterranean  intrusions  of  molten 
rock  is  not  fully  recognized.     When  the  fact  that  dikes. 


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intruded  sheets,  plutonic  plugs,  Inccolitcs,  subtuberant 
in(juntain.s,  and  volcanoeH  result  from  variations  in  one 
general  process,  is  admitted,  and  it  seems  to  me  the  con- 
clusion is  well  founded,  this  general  view  at  once  does 
away  with  the  assumption  that  steam  is  the  sole  cause 
of  volcanic  phenomenon.  These  same  considerations  must 
lead  us  to  put  aside  the  long-cherished  hypothesis  that 
there  is  an  essential  and,  to  volcanoes,  a  vital  connection 
between  extrusions  of  molten  rock  and  the  distribution 
of  surface  water-bodies. 

In  all  of  the  hypotheses  that  have  been  advanced  in 
which  steam  is  considered  as  the  prime  motor,  the  point 
of  view  is  that  obtained  by  an  observer  looking  down  into 
craters  like  those  of  Vesuvius  or  Stromboli,  when  in  mild 
activity.  The  phenomena  of  the  boiling  of  the  liquid  lava 
and  the  escape  of  great  bubbles  of  steam  are  then  the 
prominent  facts.  To  account  for  the  steam  observed  in 
such  cases,  seems  to  be  the  chief  feature  of  the  problem ; 
the  rise  of  the  molten  lava  from  miles  below  the  surface, 
the  conditions  under  which  it  exists  in  the  reservoir  from 
which  it  flows,  and  the  changes  it  undergoes  as  it  nears  the 
place  of  discharge,  are  lost  sight  of  in  the  presence  of  the 
striking  activity  in  progress  at  the  summit  of  the  lava 
column. 

If  in  imagination  we  change  the  point  of  view,  and  see 
the  reservoir  miles  below  the  surface,  the  conduit,  perhaps 
with  many  branches  leading  upward,  the  upward  flow  of 
the  molten  rock  through  the  conduit,  the  descent  of  sur- 
face water,  —  and  also  the  presence  of  water  in  stratified 
beds,  —  to  meet  the  rising  magma,  etc.,  it  must  appear 
that  the  "  sole  essential  phenomena  "to  be  accounted  for 
are  not  the  presence  of  steam. 


*■!!; 


CHAPTER  YIII 


''1 

H 


THE  LIFE  HISTORY  OF  A  VOLCANIC  MOUNTAIN 

One  of  tlie  pliases  oi  modern  geograpliical  .study  is  the 
tracing  of  the  successive  changes  that  the  various  feat- 
ures of  the  hind  pass  through  from  their  initiation  to 
their  disappearance.  As  is  well  known,  even  the  most 
magnificent  mountjiins  that  give  diversity  to  the  earth's 
surface  at  the  present  day,  have  had  their  time  of  jjirth 
and  growth,  and  have  perhaps  reached  full  maturity,  ))ut 
are  one  and  all  crumbliui^  before  the  attacks  of  the  de- 
structive  agencies  of  the  atmcjsphere  and  will  ultimately 
be  removed.  The  record  of  such  a  series  of  changes  in 
topographic  forms  from  youth  to  maturity,  old  age  and 
final  disappearance,  may  with  propriety  be  termed  a  life 
history. 

The  life  history  of  a  volcanic  mountain  should  evidently 
begin  with  the  changes  deep  within  the  earth  that  lead  to 
its  birth.  These  prenatal  causes,  however,  are  such  an 
intimate  part  of  a  still  greater  history  —  the  development 
of  the  earth  itself  —  that  it  would  lead  too  far  from  our 
immediate  theme  to  begin  a  review  of  the  history  of  a 
volcanic  mountain  with  a  discussion  of  the  conditions 
which  antecede  its  appearance  as  a  topographic  feature. 

When  a  fissure  is  formed  in  the  earth's  crust  through 
which  molten  rock  is  forced  upward  to  the  surface,  there 
may  be  an  overflow  throughout  a  considerable  extent  of 
the  break  and  a  fissure  eruption  ensue  ;  but  more  commonly 

327 


I 


'\     ■  J 


n 


328 


VOLCANOKS   or   NOKTH    AMERICA 


the  escape  of  lava  is  restricted  to  certain  circumscribed 
localities  about  whicli  volcanic;  inonntains  are  built  up. 
Whether  a  volcano  shall  belong  to  the  (juiet  or  the  explo- 
sive type  depends  on  various  conditions,  some  of  which 
have  been  discussed  in  the  preceding  cluqjters.  Volcanic 
erujjtions  thus  i)resent  great  diversity  and  lead  to  topo- 
graphic changes  with  widely  varying  characteristics.  A 
complete  di.scussion  of  the  lifj  histories  of  the  many  topo- 
graphic types  due  to  igneous  extensions  would  embrace 
the  origin,  dissection,  and  disappearance  of  vast  lava  i)lains 
like  those  dramed  by  the  Columbia ;  the  birth,  growth, 
decline,  and  death  of  mighty  domes  with  plateau-like 
summits  of  the  Hawaiian  type,  and  of  the  conical  piles  of 
lapilli  and  scoria  represented  by  the  sacred  mountain  of 
Japan.  It  is  difficult  to  group  such  varied  phenomena  in 
a  single  picture.  Let  us,  instead,  select  a  single  individual 
from  the  most  numerous  class  of  volcanic  mountains, — 
the  composite  cones  formed  largely  of  projectiles,  but 
bound  together  by  lava  streams  and  dikes,  —  and  endeavor 
to  review  the  principal  changes  it  experiences  during  its 
life  span. 

It  is  possible  that  the  aborigines  of  the  Pacific  coast 
witnessed  the  advent  of  some  of  the  giant  volcanic  peaks 
which  now  give  dignity  and  grandeur  to  the  scenery  of 
that  promising  land.  Could  we  have  stood  with  some 
primitive  hunter,  armed  with  flint-pointed  arrows  and 
stone  axe,  on  the  granite  hills  commanding  a  view  of  the 
fair  Tertiary  plains  of  Oregon  and  Washington,  we  would 
have  beheld  a  sylvan  scene  as  beautiful  in  its  varied 
charms  as  any  landscape  our  broad  continent  presents 
to-day.  Let  us  take  such  a  backward  journey.  To  the 
flight  of  fancy  a  million  years  are  but  as  a  day. 


wmmm 


nil:  Line  iiistouv  of  a  volcanic  mointain 


:{:2i> 


From  our  coiiiiimiiding  station  on  the  Tortiarv  uplands, 
furest-covurc'd  liills  and  hroad  verdant  valleys  are  spread 
before  us.  A  gleam  as  of  burnished  silver  here  and  there 
amid  the  dense  forest  of  the  plain  marks  the  course  of  a 
noble  river.  I^akes  eiudosed  by  walls  of  verdure  add  an 
indescribable  charm  to  the  scene.  Between  the  banks  of 
purple  formed  by  the  distant  hills,  we  catch  glimi)ses  of 
the  shiinuiering  sea.  The  general  features  of  the  broad 
hmdscape,  the  shadows  of  passing  clouds  on  the  summer 
foliage,  and  the  ever-varying  tints  of  sea  and  sky  are  the 
same  as  the  dwellers  A  the  earth  see  to-day,  —  and  yet 
do  not  .see,  so  familiar  are  they.  liut  little  in  the  viiried 
details  of  the  scenes  about  us  is  familiar,  except  the  crys- 
tals in  the  granite  beneath  our  feet.  Should  we  descend 
from  our  chosen  station,  we  would  find  that  the  trees  and 
flowers  in  the  forest  are  strange  to  us.  The  birds  and 
insects  that  fill  the  air  with  music  are  all  unfamiliar.  The 
mammals  that  roam  the  forest  and  haunt  the  river  banks 
and  lake  shores  are  still  more  novel.  We  have  gone  so 
far  back  in  the  history  of  the  earth  that  the  i)lants  and 
animals  are  the  ancestors  of  the  present  flora  and  fauna  ; 
yet  the  Tertiary  is  only  the  day-before-yesterday  of 
geology.  We  are  in  the  sunny  summer-tide  of  the  earth 
wliicli  preceded  the  Glacial  winter. 

Our  reveries  are  broken  by  an  earthquake  shock.  A 
fissure  has  opened  in  the  broad,  forested  plain,  and  a  vast 
column  of  vapor  is  rolling  heavenward.  Explosions  hurl 
great  rocks  high  in  the  air,  some  of  which  fall  in  the 
adjacent  forest.  The  vapor  column  is  darkened  by  dust, 
which  drifts  away  before  the  wind,  and  for  miles  to  lee- 
ward the  vegetation  is  whitened  as  if  by  snow.  The 
trees  are  denuded  of  their  branches  and  in  places  buried 


v. 


I 


i 


I'll  i   ( 


Kn 


i 

:' 

330 


VOLCANOES    OK    NOIITII    AMKKKA 


from  si^ht.  A  roar  mm  if  of  iiiinjL;;l('(l  tliiiiKlur  craslies 
makes  the  air  vibrate.  With  uacli  explosion  the  earth 
trembles.  The  cloud  of  dust-laden  va^jor  expands  and 
soon  the  entire  land  is  in  shadow.  As  the  air  ^rows 
dense  about  us,  the  sun  assumes  strange  hues.  Lightning 
(lashes  seem  to  tear  the  dense  veil  asunder,  but  the 
aocom[)anying  thundei'  is  lost  in  the  deafening  roar  of 
escai)ing  steam  and  the  crash  of  coimtless  ex[)Iosions. 
Altliough  it  is  midday,  the  blackness  of  a  starless  mid- 
night .soon  conceals  the  dreadful  scene.  Strange  cries  of 
terror-stricken  beasts  come;  from  the  neighboring  forest. 
Birds  of  unfamiliar  i)lumage,  regardless  of  our  presence, 
perch  on  the  rocks  about  us.  Our  Indian  companion 
prostrates  himself  in  woiship. 

Days  pass  before  the  sun  again  ai)pears  and  reveals  a 
scene  of  death  and  desolation  where  before  all  Avas  life 
and  beauty.  Where  the  vapor  was  first  seen  to  rise, 
there  is  a  conical  hill  of  black  iind  still  steaming  rocks, — 
an  infant  volcanic  mountain.  In  its  summit  we  can 
discern  an  opening  or  crater,  from  which  a  great  volume 
of  steam  is  rolling  out.  Occasionally  the  vapor  column 
is  darkened  by  dust  and  scoria  shot  upward  by  explosions 
within  the  crater.  During  periods  of  decreased  activity 
we  might  walk  over  the  desolate  plain  of  lapilli  and  dust, 
and  if  a  strong  wind  should  be  blowing,  climb  the  wall 
of  the  crater  and  look  down  upon  the  red-hot,  liquid  rock 
that  surges  in  its  depths.  At  night  the  light  from  tiie 
molten  lava  is  reflected  by  the  cloud  above  it.  The 
under  surface  of  the  expanded  summit  of  the  vapor 
colunm  is  all  aglow  with  lurid  light,  while  the  undulat- 
ing upper  surface  is  dark  or  perhaps  has  ;  silvery  white- 
ness in  the  moonlight. 


THK    LIFE    HI.STOIIV    OF    A    VOLCANIC    MOI'NTAIN 


Ml 


At  Viiryin<i;  intervals  for  years  the  activity  uitiiiii  tlio 
cratci"  lu'coiues  niorc  iiitt'iiso.  Tiio  iiioltiMi  rock  rises  to 
the  lowest  place  in  the  rim  of  the  crater  and  sends  a  fiery 
stream  down  its  side  and  far  out  on  tlie  i)lain.  Kxplosive 
erui)tions  occur  from  time  to  time,  and  again  and  again 
lava  wells  out,  s(jmetimes  in  such  volume  as  to  deluu'e  th(» 
surrounding  country.  Steam  rises  from  the  hroad  lava 
fields,  and  at  night  they  glow  with  a  didl  reddish  light. 
With  each  erupti(>u  the  hill  is  huilt  higher,  and  at  length 
attains  the  dignity  of  a  mountain. 

The  volcaniit  mountain  is  a])j)roaching  maturity.  It 
rises  with,  all  the  symmetry  and  freshness  of  youth,  as  a 
cone  with  long,  smooth,  gently  concave  slopes,  which 
merge  imperceptihly  with  the  surrounding  ])lain.  Ahove 
its  sharp  summit  a  cloud  is  usually  visihle  which  the 
winds  dist<jrt  into  many  fantastic  shapes. 

After  centuries,  marked  by  mild  eru})tions,  with  long 
intervals  of  rest,  the  cloud  disappears  frcjm  the  moun- 
tain's summit,  and  the  snow  lies  deep  on  its  sides  even  in 
midsummer.  The  life  of  the  volcano  seems  co  be  ended, 
and  the  mountain  to  have  reached  its  full  stature.  But 
earthquakes,  mild  at  first  and  gradually  growing  more 
and  more  severe,  indicate  that  renewed  enei-gy  has  been 
given  to  the  plutonic  agencies  deep  within  the  earth. 
Suddenly,  without  definite  warning,  the  land  in  every 
direction  is  shaken  by  severe  earthquakes  which  succeed 
each  other  quickly.  Then  comes  a  mighty  crash.  The 
earth  seems  shaken  to  its  centre.  The  land  is  again 
shrouded  in  darkness.  When  the  gloom  lessens,  we  find 
that  the  symmetrical  mountain  has  been  shattered.  Its 
summit  for  a  third  of  its  height  has  ])een  blown  away, 
and   the  rocks  of  wdiich  it  was   composed   disintegrated 


I 

•  l 


II 


) 


VOLCANOKS   OK   NOIlTH    AMERICA 


i; 


1 


M< 


I   I, 


u    4 


uiid  scattL'red  us  lapilli  aiid  dust  over  tliousands  of 
scjiiaro  miles  of  land  and  sea. 

The  mountain  is  now  a  truncated  cone  with  a  bowl- 
shaped  depression  in  its  sunnnit,  three  or  four  miles  in 
diameter  and  over  2000  feet  deep.  Of  such  shape 
and  size  was  Vesuvius  in  tlie  time  of  Spartacus.  Great 
as  has  been  the  catastrophe,  the  life  of  the  moun- 
tain is  not  ended,  but  instead  has  renewed  its  youth. 
Activity  marked  by  both  explosive  eruptions  and  lava 
llows  ensues.  A  new  cone  rises  within  the  vast  crater 
Jind  in  time  overtoi)S  its  run.  Renewed  eruptions  re- 
build the  mountain.  Tt  becomes  higher  and  of  grander 
pro] portions  than  before  the  great  explosion  that  truncated 
its  summit,  but  renmants  of  the  rim  of  the  great  crater 
can  be  detected  at  certain  localities  on  its  sides. 

Centuries  pass  without  marked  changes,  ])ut  a  slow 
decline  of  energy  is  manifest.  Lava  no  longer  llows  from 
the  crater.  The  apex  of  the  cone  is  sharp.  The  lower 
slopes  are  forest-covered. 

Earthquakes  again  agitate  the  earth.  The  lofty  moun- 
tain is  rent  by  fissures,  some  of  which  extend  from  its 
base  to  near  the  summit.  ^lolten  lava  pours  out  through 
these  openings  and  feeds  surfat.  j  flows  which  devastate  the 
adjacent  forest.  Some  of  the  molten  rock  cools  in  the 
fissures  and  forms  dikes,  which  serve  to  bind  together 
the  broken  lava  sheets,  and  give  greater  strength  to  the 
structure. 

More  quiet  conditions  ensue.  Explosions  become  in- 
frequent and  finally  cease.  The  mountain  has  a  height 
of  over  15,000  feet.  The  vapor  cloud  that  continues  to 
rise  from  it  for  centuries  after  the  last  eruption  may  be 
seen  for  hundreds  of  miles  when  the  air  is  clear.     The 


tmommmMS:  OMir 


TIIIJ    ..IKE    HISTORY   OV    A    VOLCANK;    MOrXTAIX 


mi 


vast  pile,  that  lias  required  tens  of  thousands  of  years 
for  its  upljuilding,  has  reached  its  majority.  It  ranks 
with  the  greater  of  tlie  volcanic  inountains  of  the  earth. 
It  is  well  built.  Its  form  is  one  of  great  stability.  Ap- 
parently it  will  endure  as  long  as  the  world  lasts.  Ihit 
wait.  Soft  vapor  wreaths  gather  silently  about  its  sides. 
Rain  falls.  During  all  of  the  time  that  the  mountain 
has  been  growing,  there  have  been  destructive  agencies 
at  work,  but  their  eft'ects  have  been  more  than  counter- 
acted by  the  energy  of  the  plutcjiiic  forces  striving  to 
build  a  monument  to  their  memory. 

The  once  molten  rock  forming  the  great  mountain 
becomes  cold,  except  deep  in  the  interior.  The  hard 
lava,  as  well  as  the  loose  lapilll,  crumbles  to  s<jil,  and 
forests  once  more  clothe  the  mountain  sides.  Near  the 
line  marking  the  upper  limit  of  tree  growth,  there  are 
broad  grass-covered  areas  with  scattered  groves  of  hardy 
evergreens.  The  knolls  and  glades  in  these  natural 
parks  are  brilliarit,  with  flowers.  Above  the  broad 
belt  of  alpine  plants,  which  surrounds  the  mountain 
like  a  garland,  are  glittering  snow  fields.  A  dark 
line  at  the  summit  of  the  cone  indicat  \s  that  the  rocks 
forming  the  rim  of  the  crater  are  still  sufficiently  warm 
to  melt  the  snow  that  falls  upon  them.  Vapor,  con- 
densed from  passing  air  currents,  forms  cloud  banners 
about  the  summit  which  drift  away  in  shining  folds 
and  resemble  the  clouds  that  formerly  arose  from  the 
steaming  rocks.  In  winter  the  vast  pyramid  is  of  spot- 
less white,  relieved  by  delicate  blue  shadings  where  the 
shadows  lie.  As  time  passes,  the  snows  become  more 
abundant,  and  even  in  summer  much  of  the  mountain 
is  robed  in  white.     The  snovr  hardens  into  ice.     Glaciers 


hi 


11 


1 1 


I, 

I''  ' 

r 


i'l 


i 

I 


Li 


Hi 


Siii 


111 


.^''   I 


384 


VCJLCAXOKS    OF    XOUTH    AMEUICA 


are  born,  and  slowly  carve  deep  channels  and  l)road 
amphitheatres.  The  mountain  has  passed  its  prime  and 
is  gradually  yielding  to  the  ceaseless  iittacks  of  the  de- 
structive agencies  of  the  air. 

The  sununit  is  no  longer  sharp,  but  blunted,  and  re- 
veals the  convex  curvature  characteristic  of  weathered 
rocks.  Erosion  is  most  intense,  however,  midway  down 
the  slopes,  and  it  is  there  tlie  greatest  changes  appear. 
The  sides  of  the  mountain  are  no  longer  graceful,  con- 
cave curves.  The  streams  of  hardened  lava  become 
prominent  as  the  softer  rocks  about  them  are  removed. 
The  dikes  are  brought  into  relief  in  a  similar  way,  and 
form  narrow  ridges  that  may  be  traced  from  near  the 
summit  down  the  slopes  and  far  out  on  the  adjacent  plain. 

For  a  long  time  in  the  past  maturity  of  the  mountain, 
the  loose,  unconsolidated,  fragmental  products,  of  which 
it  is  largely  composed,  withstand  the  erosive  agencies 
in  a  r'MTiarkable  manner.  The  secret  of  this  is  that 
these  loose  accumulations  allow  water  to  percolate  freely 
through  them  and  thus  rob  it  of  the  power  to  erode. 
The  rock  fragments  near  the  surface  are  broken  still 
finer  by  changes  of  temperature  and  by  the  freezing  of 
absorbed  water.  But  they  yield  principally  and  to  a 
great  depth  to  solution.  The  percolating  waters  are 
charged  with  acids  derived  mainly  from  volcanic  exha- 
lati(jns,  which  enhance  their  solvent  power.  The  rocks 
are  leached  of  their  more  soluble  minerals  and  become 
friable  and  soft.  The  fine,  clay-like  material  left  by 
this  process  as  a  residue  fills  the  interspaces  between 
tile  larger  fragments,  thus  checking  percolation  and 
admitting  of  the  gathering  of  the  surface  waters  into 
rills  and  brooks.     Erosion  then  becomes  more  active,  and 


THE   LIIi;'    HISTOIIY    OF    A    VOLCANIC    MOINTAIN 


channels  and  ravines  are  carved  Avliich  increase  the  diver- 
sity of  the  mountain's  sides. 

Absorbed  in  watching  the  growth  of  the  mountain 
and  the  carving  of  the  lines  that  mark  its  advancing 
age,  we  have,  i)erhaps,  l)een  unmindful  of  tlie  flight  of 
time.  The  Tertiary  age  lias  pas.sed.  A  climatic  cliange, 
gradual  in  its  approach,  luis  led  to  a  marked  increase 
in  the  size  and  extent  of  the  glaciers  flowing  from  the 
neve  fiekhi  al)out  tlie  mountain's  summit.  The  river- 
like streams  of  ice  creep  slowly  down  the  rugged  slopes 
and  advance  for  a  score  of  miles  over  the  adjacent 
plain.  From  the  extremity  of  each  glacier,  a  roaring 
torrent  of  milky  water  flows  away  through  a  trencli-like 
valley.  The  mountain  is  white  from  base  to  suunnit 
throughout  the  year.  The  forests  that  formerly  clothed 
its  sides  have  been  swept  away.  For  tens  of  centuries 
the  slowly  moving  ice  grinds  away  the  rocks,  and 
great  changes  in  topography  are  in  progress.  The  neve 
fields  about  the  higher  portions  of  the  peak  divide,  as 
they  descend,  into  well-defined  glaciers,  each  of  which 
deepens  its  channel  and  intrenches  itself  in  the  rocks. 
The  spaces  between  the  radiating  canyons  excavated  hy 
the  glaciers  stand  in  bold  relief  and  appear  as  huge 
triangles  arranged  about  the  base  of  the  mountain. 
Each  of  these  surfaces  spared  by  the  ice  erosion  pre- 
sents a  sharp  angle  to  the  descending  current  of  the 
neve  and  divides  it  as  the  prow  of  a  vessel  ancliored 
in  a  stream  divides  the  passing  current.  As  the  glaciers 
grind  deeper,  the  upward-pointing  angles  of  the  inter- 
vening wedges  become  more  and  more  prominent,  and 
at  length  appear  as  secondary  peaks,  midway  np  the 
slopes  in  which  the  bordering  canyons  have  been  carved. 


i 


I  i 


sm 


VOLCANOES   OF    NOllTll    AMEUICA 


II M 


ffl  !• 


Within  the  circle  formed  by  these  secondary  spires  and 
crags  rises  the  steep-sided  central  dome. 

The  geological  winter,  termed  the  Glacial  period,  slowly 
passes.  The  glaciers  become  smaller  and  shrink  within 
the  canyons  they  have  carved.  In  sunnner  bare  rocks 
appear  on  the  lower  slopes  of  the  mountain,  but  centuries 
pass  before  the  forest  again  advances  and  conceals  the 
desolation  and  ruin  the  ice  has  caused.  Flowers  again 
enamel  the  alpine  meadows,  but  the  great  dome  above  is 
white  with  perennial  snow. 

Our  mountain  has  passed  its  prime  and  bears  the 
unmistakable  furrows  of  age,  but  is  still  majestic.  It  has 
reached  the  stage  in  its  life  history  illustrated  at  the 
present  day  by  Mt.  Shasta  and  its  companion  in  magnifi- 
cence, Mt.  Rainier. 

With  the  slow  transformation  of  the  mountain  changes 
have  taken  place  in  the  surrounding  plain.  The  lava 
streams  which  flowed  from  the  volcano  during  its  time 
of  growth,  and  sought  the  lowest  depressions  in  the  land 
about  its  base,  have  been  left  in  bold  relief  by  the  removal 
of  the  softer  rocks  not  protected  by  them,  and  now  appear 
as  prominent  tablelands.  Beneath  the  clitt's  of  columnar 
basalt  forming  the  boundaries  of  these  mesas  the  vol- 
canic dust  and  lapilli  is  exposed,  which  was  strewn  over 
the  land  during  the  earlier  eruptions.  On  searching  in 
these  deposits  we  can  find  trunks  and  stumps  of  trees,  relics 
of  the  Tertiary  forests,  now  changed  to  stone.  Possibly 
a  bone  of  some  strange  mammal,  long  since  extinct,  may 
also  reward  our  search.  The  teachings  of  these  relics  of 
ancient  floras  and  faunas  are  in  harmony  with  the  ruin 
of  the  once  mighty  mountain,  and  also  bear  testimony  to 
the  great  lapse  of  time  since  our  volcano  was  young. 


uj: 


1 


THE    LIFE    UlSTOllV    OK    A    VOLCANIC    MOINTAIN 


;537 


The  study  of  iiuuiy  volcanic  mountains  in  various 
stages  of  dilapidation  and  decay  enaiiles  one  to  predict 
the  principal  phases  that  our  ideal  mountain  Avill  pass 
through  in  its  old  age.  A  century  witnesses  but  little 
change  in  its  contours  and  practically  none  in  its  height. 
But  tens  of  centuries  will  see  the  outer  covering  of  scoria 
and  lapilli  slowly  removed.  The  ice-filled  amphitheatres 
on  its  sides  will  be  enlarged.  The  lateral  ridges  separat- 
ing them  will  become  sharp,  ragged  crests,  and  then 
crumble  to  feed  the  moraines  at  their  sides.  The  back- 
ward cutting  of  the  amphitheatre  and  canyon  will  give 
steep  sides  to  the  central  dome,  and  at  length  the  convex 
summit  due  to  weathering  will  be  br(jken  and  spires  and 
crests  at  a  lower  level  take  its  place.  As  the  mountain 
decreases  in  height,  the  glaciers  that  have  done  so  much 
toward  sculpturing  its  sides  will  shrink  and  disappear. 
The  central  core  of  hard  lava  will  be  left  in  relief  as  the 
softer  rocks  about  it  are  removed,  and  become  a  promi- 
nent topographic  feature.  For  ages  this  central  plug  of 
resistant  rock  will  stand  as  a  mighty  tower  bidding  defi- 
ance to  storms  and  frosts,  and  resemble  the  volcanic  necks 
now  forming  such  a  marked  feature  of  the  arid  region 
about  Mt.  Taylor,  New  Mexico.  Our  mountain  will  then 
have  reached  extreme  old  age.  In  fact,  as  a  mountain, 
its  fife  will  already  have  ended.  The  tower-like  mass 
formed  by  the  central  plug  will  slowly  ci'umble,  and  at 
length  a  rounded  hill  with  weathered  boulders  at  the  top 
will  be  all  that  is  left.  The  destructive  agencies  of  the 
atmosphere  are  unsparing,  however,  and  even  this  humble 
monument  to  the  memory  of  the  once  glorious  monarch 
must  be  removed. 

Should  the  platform  on  which  the  mountain  was  built 


#"* 


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338 


VOLCANOES   OF   NOUTH    AMERICA 


be  Hiifficieiitly  elevated  above  tlie  sea,  or  if  earth  move- 
ments during  the  long  history  we  have  briefly  reviewed 
liave  upraised  it,  erosion  will  cut  away  the  rocks  to  :u\ 
horizon  below  that  of  the  valley  in  which  the  volcano  had 
its  birth,  and  reduce  the  entire  region  to  the  level  of  the 
sea.  In  other  words,  the  land,  with  whatever  topographic 
forms  it  may  have  possessed,  will  be  eroded  to  base  level. 
A  geographical  cycle  will  then  have  come  to  an  end. 
Some  thoughtful  man  in  the  far  distant  future  will  walk 
over  the  plain  beautiful  with  a  new  flora,  and  find  the 
dikes  of  plutonic  rock  that  occupy  the  Assures  in  the 
earth's  crust  from  which  came  the  material  used  in  build- 
ing the  vanished  mountain. 


•'*■ 


m 


INDEX 


Aa  surfaces  of  lava  streans,  59-02. 
Ahif'S  rdigiiisa,  mention  of,  170. 
Acid  lavas,  fusibility  of,  'u,  58. 
Acid  rocks,  term  explaim-d,  li:). 
Adams,  .Mt.,  \Va.sh.,  brief  account  of, 

2.'J9,  240  ;  hei.ijht  of,  2:!4. 
Agates,  origin  of,  04. 
Agua,  Volcan  de,  description  of,  108- 

171. 
Aguilera,  J.  S.,  cited  on  volcanoes  of 

Mexico,  170,  181. 
Ahuacatlan,  description  of,  189. 
Akutan,   Alaska,    eruptions    of    dust 

from,  79. 
Alaska,  deposits  of  volcanic  dust  in, 

288,  289  ;  volcanoes  of,  2(')7-28;i. 
Alece    Springs,   Australia,    sound    of 

eruption  of  Krakatoa  heard  at,  27. 
Aleutian  Islands,  central  and  western, 

volcanoes  of,  282. 
Aleutian  volcanic  belt,  description  of, 
■     268-270. 

Amygdaloid,  nature  and  origin  of,  64. 
Analysis  of  the  gases  of  volcanoes,  62. 
Analyses  of  volcanic  dust,  292. 
Anderson,  Capt. ,  cited  on  Bogosloff ,  280. 
Andesite,  brief  account  of,  124,  126. 
Arizona,  volcanic  mountains  of,  192, 

193. 
"Ashes,"  volcanic,  a  misnomer,  75. 

Baker,  Mt.,  Wash.,  brief  account  of, 
245,  240  ;  height  of,  2'^1. 

Bangkok,  Siani,  sound  of  eruption  of 
Krakatoa  heard  at,  27. 

Barbour,  E.  II.,  cited  on  volcanic  dust, 
280. 

Basalt,  brief  account  of,  121,  122. 

Basaltic  structures,  in  dikes,  illus- 
trated, 97,  98. 

Basic  lavas,  fusibility  of,  57,  58. 

Basic  rocks,  term  explained,  113. 


Becker,  G.  F.,  cited  on  the  profiles  of 

volcanic  mountains,  82. 
Biihveli,  Lake,  Cal.,  reference  to,  2.'1]. 
Ilig  Horn  Mountains,  cited  as  an  ex- 
ample of  subtuberant  mountains,  l(i4. 
lUackfoot  basin,  Idaho,  basaltic  craters 

in,  258. 
Black  Hills,  Dakota,  cited  as  an  exam- 
ple of  subtuberant  mountains,  104  ; 

plutonic  jilugs  near,  102. 
Blomidon,   Nova   Scotia,  reference  to 

rocks  of,  121. 
Bogosloff   Island,   Alaska,  description 

of,  270-281. 
Bombs,  volcanic,  nature  and  origin  of, 

T.i,  74. 
Bonneville,   Lake,    mention    of,    198, 

202,  205. 
Bonney,  E.  \V.,  cited  on  volcanic  dust 

from  Cotopaxi,  79. 
Boulders  of  disintegration,  reference 

to,  98. 
Brakleast   Hill,   Mass.,  volcanic  dust 

from,  290. 
Breccia,  definition  of,  00. 
Brigham,  W.  'P.,  cited  on  volcanoes  <if 

Central  America,  137. 

Calaniahue,  Mt.,  Mex.,  mention  of,  190. 

Calder,  Mt.,  Alaska,  mention  of,  208. 

Canada,  volcanic  rocks  of,  206,  207. 

Canadian  River,  N.  M.,  lava  flow  in, 
204. 

Canyon  City,  Col.,  volcanic  cones 
near,  250. 

Cantwell,  J.  C,  cited  on  Bogosloff,  278. 

Cascade  Mountains,  brief  account  of, 
246. 

Cebomco,  Mex.,  description  of,  189. 

Central  America,  catalogue  of  volca- 
noes of,  l.'J7-1.39  ;  volcanoes  of,  de- 
scribed, 134-171. 


339 


mm 


'"'wm 


mm 


mm 


840 


INDEX 


Cha^'oz  Islands,  sound  of  eruption  of 

Knikatoa  heard  at,  27. 
CliaracterislicH  of  the  products  of  vol- 


■i  , 


'i  \ 


i'ii' 


'i        ti 


ii.i 


canoes,  48-80. 


Characteristics  of  volcanoes,  1-120. 

Chnrlen  Bal,  the  vessel,  near  Krakatoa, 
24. 

Chatard,  T.  M.,  analysis  of  volcanic 
dust  by,  202. 

Chemical  hypothesis  of  origin  of  vol- 
canoes, .']1!). 

Cinder  Cune,  Cal.,  description  of, 
228-231  ;  sketch  of  crater  of,  2.J1. 

Citlal-tepetl.     See  Orizaba. 

Ciudiid  Vieja,  Guatemala,  reference  to 
destruction  of,  170. 

Classiflcation  of  igneous  rocks,  111-118. 

Clavigero,  Abb^,  mention  of,  153. 

Cleveland,  Mt.,  Alaska,  mention  of, 
282. 

Coast  range,  volcanoes  of,  257. 

Cofre  de  Perote,  Mex.,  description  of, 
180-188. 

Colima,  Mex.,  description  of,  188, 
180. 

Columbia,  list  of  volcanoes  in,  137. 

Columbia  lava,  brief  account  of,  30 ; 
description  of,  260-267 ;  reference 
to,  06,  121. 

Columbia  River,  ice  dam  in  canyon  of, 
250. 

Columnar  structure  in  dikes,  illus- 
trated, 07,  08. 

Columnar  structure  of  Columbia  lava, 
251. 

Composite  cones,  structure  of,  illus- 
trated, 87. 

Conception,  Chile,  reference  to  de- 
struction of,  103. 

Cones  formed  ox  projectiles,  86-89. 

Conseguina,  Nicaragua,  description  of, 
158-164  ;  sketch  of,  158. 

Contact  metamorphism,  reference  to, 
97. 

Cook,  Capt.,  cited  on  Bogosloft  Island, 
276. 

Cook's  Inlet,  Alaska,  volcanoes  of, 
270-273. 

Costa  Rica,  list  of  volcanoes  in,  137. 

Cotopaxi.  eruption  of  dust  from,  77- 
79. 

Coulee.,  meaning  of  the  word,  255. 

Coulee  City,  Wash.,  canyon  near,  256. 


Crater   Livke,  Ore.,  brief  account  of, 

235,  236. 
Cross,  Whitman,  cited  on   laccolites, 

103. 
Cryptocrystalline,  term  explained,  112. 

Dall,  W.  II.,  cited  on  Alaskan  volca- 
noes, 270-272 ;  cited  on  Hogoslol'f 
Island,  276 ;  cited  on  Mt.  Edge- 
cunibe,  268. 

Dana,  K.  S.,  cited  on  stalactites  in  lava 
tunnels,  69. 

Dana,  J.  D.,  cited  on  driblet  cones, 
70,  71  ;  cited  on  the  fusibility  of 
lava,  56  ;  cited  on  rate  of  tiow  of 
lava  streams,  67  ;  cited  on  "  lava 
balls,"  74  ;  cited  on  I'ele's  hair,  72  ; 
cited  on  the  profiles  of  volcanic 
mountains,  80,  81  ;  cited  on  volca- 
noes in  Coast  rjvnge,  257. 

Dana,  Mt.,  Cal.,  mention  of,  210. 

Darwin,  C,  cited  on  volcanic  bombs, 
74. 

Daubeny,  Dr.,  cited  on  chemical  origin 
of  volcanoes,  319. 

Davidson,  George,  cited  on  Mt.  St. 
Augustine,  273. 

Davy,  Sir  H.,  cited  on  chemical  origin 
of  volcanoes,  319. 

Dawson,  G.  M.,  cited  on  lava  fields  in 
Canada,  207. 

Deccan  trap,  India,  brief  account  of, 
39-43  ;  reference  to,  260. 

Denudation,  nature  of,  91. 

Deville,  S-C,  cited  on  the  gases  of 
volcanoes,  62. 

Dikes  at  the  Spanish  peaks.  Col.,  261 ; 
nature  and  origin  of,  88-90,  96-99 ; 
sandstone,  reference  to,  96. 

Diller,  J.  S.,  cited  on  Cinder  Cone, 
near  Lassen's  Peak,  Cal.,  231-2.33  ; 
cited  on  Crater  Lake,  Ore. ,  236 ; 
cited  on  Mt.  Shasta,  Cal.,  227, 
228 ;  cited  on  the  Three  Sisters, 
Ore.,  237  ;  cited  on  volcanic  dust, 
290,  291,  293,  294. 

Distribution  of  volcanoes,  124-133. 

Dollfus,  A.,  and  E.  de  Mont-Serrat, 
cited  on  Conseguina,  169,  105 ; 
cited  on  Izalco,  141  ;  cited  on  erup- 
tion of  Volcan  del  Fuego,  165-168  ; 
references  and  writings  of,  159, 
166. 


I 


INDKX 


341 


Driblet  cones,  cliaractcr  ami  origin  of, 
70,  71. 

Dust,  volcanic,  (letjosits  of,  284-21HJ  ; 
nature  and  mode  of  occurrence  of, 
7o,  7»i. 

Dutcii  Hay,  ('cylon,  sound  of  eruption 
of  Kraltatoa  lieaiil  at,  '21. 

Dutton,  C.  E.,  cited  on  tlie  aa  surfaces 
of  lava  streams,  00,  01  ;  cited  on 
Crater  Lalte,  Ore.,  lilio,  2.'{0  ;  cited 
on  Mt.  Taylor,  N.  M.,  1)>:!-1W); 
cited  on  palioehoe  surfaces  of  lava 
streams,  02,  0;j ;  cited  on  I'ele's  liair, 
72,  7;^  ;  citt  on  tiie  volcanoes  of  tlie 
Hawaiian  Islands,  ;]0-o3. 

Eartlniualtes,  rents  formed  by,  00. 

Edgecumbe,  Mt.,  Alaska,  mention  of, 
208. 

Ellensburg,  Wash,,  dikes  near,  2.")2, 

Emmons,  S.  F.,  ascent  of  Mt.  Kainier, 
Wash.,  by,  242-245;  cited  on  Mt. 
St.  Helen's,  Wash.,  240;  cited  on 
Mt.  Pitt,  Ore.,  2:!0  ;  and  A.  Hague, 
cited  on  Ragtown  ponds,  Nev., 
200. 

Endlich,  F.  M.,  cited  on  the  Spanish 
peaks,  Col.,  200,  201  ;  cited  on  vol- 
canic cones  in  Colorado,  2u8,  259. 

Erosion  of  volcanic  mountain?,  90-04. 

Etna,  Mt.,  mention  of,  1  ;  reference  to 
fissures  in  the  sides  of,  37;  extruded 
and  intruded  igneous  rocks,  00. 

Felsite,  term  explained,  112. 

Ferrer,  cited  on  height  of  Orizaba, 
173. 

Fissure  eruptions,  Columbia  lava  from, 
252  ;  description  of,  30-43. 

Flagstaff,  Arizona,  volcanic  mountains 
near,  102,  193. 

Flames  accompanying  volcanic  erup- 
tions, 51. 

Fouqu6,  cited  on  gaseous  products  of 
volcanoes,  49. 

Fragmental  products  of  volcanoes,  69- 
80. 

Fuego,  Volcan  del,  Guatemala,  de- 
scription of,  104-108. 

Fumarole  stage  in  volcanoes,  brief  ac- 
count of,  46. 

Fumaroles,  on  Izalco,  San  Salvador, 
140. 


Fusibility  of  lava,  causes  of  variation 

in  the,  50. 
Fusiyama,  Japan,  reference  to,  81. 

Gabb,  W.  M.,  cited  on  volcanoes  of 
Central  America,  130. 

Galindo,  Juan,  cited  on  eruption  of 
Conseguina,  102. 

(laseous  products  of  volcanoes,  49-53. 

(iases  of  volcanoes,  analysis  of,  52. 

Geological  survey  of  ("anada,  reference 
to,  200. 

Geikie,  Archibald,  cited  on  Columbia 
lava,  255  ;  cited  on  gaseous  products 
of  volcanoes,  51  ;  cited  on  lava  Helds 
of  Eurojie,  43. 

Giant's  Causeway,  Ireland,  reference 
to,  121,  251. 

Giblis,  George,  cited  on  Mt.  Hood,  230, 
240. 

Gilbert,  G.  K.,  cited  on  the  Ice  Spring 
craters,  Utah,  198-202  ;  cited  on  lac- 
colitfs,  10.'» ;  cited  on  volcanic  moun- 
tains of  Arizona,  102. 

Glacial  deposits  in  Central  Washing- 
ton, 2'i0. 

Glaciers  of  North  America,  reference 
to,  225. 

Golden,  Col.,  volcanic  cones  wear,  250. 

Gorman,  M.  W.,  cited  on  Mt.  Hood, 
238  ;  cited  on  Mt.  St.  Helen's,  241. 

Grand  Coulee,  Wash.,  brief  account 
of,  250. 

Granite,  brief  account  of,  118-121. 

Grant,  U.  S.,  cited  on  volcanic  dust, 
289. 

Great  Plains  of  the  Columbia,  255. 

Grewingk,  C,  cited  on  Alaskan  vol- 
canoes. 270. 

Guatemala,  list  of  volcanoes  in,  130. 

Hague,  Arnold,  cited  on  Mt.  Hood, 
Ore.,  230  ;  and  S.  F.  Emmons,  cited 
on  Ragtown  ponds,  Nev.,  200. 

IIa»vaiian  Islands,  aa  surfaces  of  lava 
streams  on,  50-62  ;  brief  description 
of  volcanoes  of,  29-36  ;  reference  to 
rocks  of,  121. 

Hawaiian  volcanoes,  eruptions  of  lava 
from,  55 ;  rate  of  flow  of  lava  from, 
57. 

Hayes,  C.  W.,  cited  on  volcanic  dust 
in  Alaska,  288. 


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1NI>KX 


Ilealy,  M.  A.,  cilcil  (m  IJdnosloff,  278. 

Hfiif  of  till'  iiitt'iior  of  tlic  cartli,  2'.I7. 

ll(il|ii-iii,  Aiii{ulo,  cited  on  uNciiit  of 
Orizaba,  Mex.,  17u,  170  ;  cited  on 
h('if,'l»t  of  Orizaba,  Mex.,  174;  cited 
on  volcanoes  of   Mexico,    170,   180, 

Henry  Monntains,  I'tali,  cited  as  type 
of  laccolitts,  lo;i. 

Herculaneuni,  Italy,  reference  to  de- 
strnction  of,  10. 

Hdlyoke,  Mt.,  Ma.ss.,  reference  to  rocks 
of,  121. 

Honduras,  li.st  of   volcanoes  in,  1.'18. 

Hood,  Mt.,  Ore.,  brief  account  of,  237, 
238  ;  liei-ht  of,  234. 

Hook  Mountains,  N.  Y.,  reference  to, 
101. 

Hot  springs,  origin  of  tlie  heat  of,  48. 

Humboldt,  A.  von,  cited  on  height  of 
Orizaba,  Mex.,  173  ;  cited  on  Izalco, 
141  ;  cited  on  .lorullo,  Mex.,  ir)2, 
163,  155  ;  cited  on  volcanoes  of  Mex- 
ico, 172,  179,  187,  188. 

Hungary,  reference  to  phonolite  hills 
of,  83. 

Ice  Spring  craters,  Utah,  description 
of,  198-202. 

Iddings,  J.  P.,  cited  on  rock  from  Mono 
Valley,  210 ;  reference  to  book  trans- 
lated by,  115. 

Igneous  intrusions,  nature  of,  94-106. 

Igneous  rocks,  characteristics  of,  100- 
120;  classification  of,  111-118. 

Iliamna  Volcano,  Alaska,  description 
of,  271. 

Ilojiango  Lake,  San  Salvador,  volcanic 
eruptions  in,  147,  148. 

Imbricated  mountains,  structure  of, 
84. 

Intermediate  rocks,  term  "explained, 
114. 

Intruded  sheets,  nature  and  origin  of, 
90-101. 

Intruded  and  extruded  igneous  rocks, 
09. 

Intrusions  of  igneous  rock,  99-106. 

Intrusive  rocks,  relation  of,  to  volca- 
noes, 301-304. 

loanna  Bogosluva,  see  Bogosloff. 

Isle  of  Staffa,  Scotland,  reference  to, 
251. 


Fxtacciluiatl,  Mex.,  description  of,  183, 

1H4  ;  height  of,  17». 
Izalco,  San  Salvador,  dt-scriptlon  and 

Idslory    of,    141-140;     mention   of, 

140. 

.Jamaica,  fall  of  volcanic  dust  in,  100. 

•Jan.ssen,  cited  in  the  gase.s  of  volcanoes, 
52. 

Jefferson,  Mt.,  Ore.,  brief  account  of, 
230,  237  ;  height  of,  234. 

John  Day  system,  reference  to,  253. 

Johnson,  VV.  1).,  map  by,  213. 

JoruUo,  Mex.,  history  of,  152-150; 
mention  of,  140 ;  San  I'edro  de, 
mention  of,  153. 

Judd,  J.  \V.,  cited  on  eruption  of  vol- 
canic dust  in  Iceland,  70,  77  ;  cited 
on  the  composition  of  volcanic  va- 
pors, 53  ;  cited  on  commercial  prod- 
ucts of  volcanoes,  4(i ;  cited  on  the 
nature  of  volcanic  eruptions,  36 ; 
cited  on  the  profiles  of  volcanic 
mountains,  82  ;  cited  on  Stromboli, 
Italy,  3-0  ;  cited  on  tiic  .structure  of 
lapilli  cones,  85 ;  reference  to  book 
by,  115,310,321. 

June  Lake,  Cal.,  glacial  and  volcanic 
records  near,  224. 

Kemp,  J.  F.,  cited  on  composition  of 
rhyolite,  124  ;  reference  to  book  by, 
115. 

Kilauea  Volcano,  Hawaiian  I.-slands, 
brief  account  of,  32-34 ;  profile  of, 
81. 

King,  C,  cited  on  Ragtown  ponds, 
Nev. ,  200. 

Krakatoa.  description  of,  22-29 ;  dust 
erupted  from,  70,  77,  290,  294  ;  ref- 
erence to  eruption  of,  104. 

Krukenborg,  C.  Fr.  W.,  cited  on  Pele's 
hair,  72. 

Labradnrite  in  basalt,  121. 

Labuan,  Borneo,  sound  of  eruption  of 

Krakatoa  heard  at,  27. 
Laccolites,  brief  account  of,  102,  103. 
Lahontan,  Lake,  mention  of,  205. 
Landivar,  Raphael,  mention  of,  153. 
Lapilli,  character  of,  75. 
Lapilli  cones,  structure  of,  illustrated, 

85. 


INDKX 


;n:j 


dust 
ref- 

'ele's 


J3. 
Ued, 


Lnsspii's    Peak,   Tal.,   description    of 

cinder  cone  mar,  li^H-^ol. 
Lava  Walla,  rcaumliiing  voleaiiie  bunilis, 

74. 
Luva    Park,    Cal,,    notice    of,    li-'tl ; 

HtreaniM.  eliaracteristics  of,  54-71. 
Le  Oonle,  Joseph,  cited  on  eartli(|uako 

ti.ssures,  \M  ;   cited   on  thiclcnes.s  of 

('(ilunil)ia  lava,  251. 
Lite  history  of  a  volcanic  mountain, 

■.',27,  :5:{H. 
Lipari  LslandH,  Italy,  mention  of,  L 
Liparite  (Uliyolite),  brief  account  of, 

1211-124. 
Livin,i;ston,.I.  W.,  olwervations  by,  150. 
Loa,  Mauua.     See  Manna  Loa. 
Lobley,  J.   L.,  cited  on  structure   of 

Vesuvius,  87  ;  cited  on  Ve.suviu.s.  17. 
LoesH,  volcanic  du.st  associated  witli, 

280. 
Lou'iin,  Mt.,  reference  to  lieii;htof,  173. 
Lower  California,  volcanoes  of,  IIK). 
Lyell,  Charles,  cited  on  Monte  Nuovo, 

14(1 ;  reference  to  works  of,  321. 
Lyell,  Mt.,  Cal.,  mention  of,  210. 

Macrocry.stalline,  term  explained,  113. 
Magma,  term  defined.  111. 
Makushin,   Mt.,  Alaska,  mention  of, 

281. 
"Mamclons"  of  the  Lsland  of  Bour- 
bon, reference  to,  83-85. 
Marvine,  Archibald,  cited  cm  volcanic 

cover  in  Colorado,  250. 
Mauna  Loa,  Hawaii,  accotnit  of,  29- 

32  ;  illustrating  a  type  of  mountains, 

80j  profile  of,  81. 
Mazama,  Mt.,  Ore.,  Crater  Lake  on, 

235,  236  ;  height  of,  234. 
Mechanical  hypotliesis  of  the  origin  of 

volcanoes,  320. 
Merrill,  G.  P.,  analysis   of    volcanic 

dust  by,  292  ;  cited  on  rocks  from 

BogoslofI,  280. 
Metamorphism,  contact,  reference  to, 

97. 
Meteoric  hypothesis,  reference  to,  297. 
Mexico,  height  of  mountains  in,  174  ; 

volcanoes  of,  172-190. 
Mono  Craters,  Cal.,  description  of,  217, 

225. 
Mono  Lake,  Cal.,   elevation  of,  210; 

reference  to  volcanoes  near,  37. 


Mono  Valley.  Cal.,  vohanic  rratcr.s  in, 
208  ;  deposits  of  volcanic  dust  in, 
285. 

Mora  Creek,  N.  M.,  lava  flow  in,  2tl4. 

.MciuntainH  formed  of  lava  sheets,  .s|, 
85. 

Muir's  butte,  Cal.,  reference  to,  257. 

Nebular  hyixithesis,  reference  to,  297. 

Necks,  volcanic,  in  New  .Mexico,  193, 
108 ;  mention  of,  93 ;  nature  and 
origin  of,  80,  90. 

Negit  Island,  .Mono  Lake,  Cal.,  tlescrip- 
tion  of,  210,217. 

Neva(h)  de  Toluca,  Mex.,  height  of, 
174. 

Newark  system,  reference  to  igneous 
rocks  in,  101,  120;  reference  to  re- 
port on,  44  ;  trap  rooks,  4.'!-45. 

New  Hogosloff.     See  Uogoslofl. 

New  Mexico,  brief  accmmt  of  the  vol- 
canoes of,  202-200  ;  volcanic  moun- 
tains of.  lO.J-198. 

Nicaragua,  li.st  of  volcanoes  in,  138. 

Nicholson,  M.  11.,  analysis  of  volcanic 
dust  by,  292. 

North  Mountain,  Nova  Scotia,  refer- 
ence to  rocks  of,  ;21. 

North  Table  Mountain,  Col.,  reference 
to,  259. 

Norwa.\',  volcanic  dust  from,  290. 

Nuovo,  Monte,  Italy,  mention  of,  140. 

OcatC  crater,  N.  M.,  brief  account  of, 

204. 
Oldham,  R.  D.,  cited     n  the  Deccan 

trap  of  India,  39-41. 
Ordofiez,   E.,   cited  on   volcanoes   of 

Mexico,  177,  181. 
Oregon,  deposits  of  volcanic  dust  in, 

287. 
Oregon    and   Washington,   great  vol- 
canic mountains  of,  233-246. 
Orizaba,   Mex.,  description    of,    173; 

height  of,  174. 
Owen,  D.  D.,  cited  on  columnar  dike, 

98. 

Pahoehoe  surfaces  of  lava  streams,  62, 

63. 
Palisade  trap  sheet,  N.  J.  and  N.  Y., 

description   of,   101;    reference   to, 

121,  251. 


1 


.344 


INDLX 


11 


!  ( 


/' 


\')' 


:i: 


I'liliiileri  L.,  cili'il  lit)  V'psuvius,  17-22. 
I'aota   IhIuikI,  Mmiii  liUkc,  t'al..  (If- 

Mcrii)ti(m  of,  211-210. 
raviildff  volcano,  AlaHkn,  iiici>iini\  of, 

realf,  A.  C,  cited  on  cruUTH  in  Hlack- 

foot  basin,  Idaho,  '2M. 
rtlt''(j   iinir,  cliaractcr  and  orifjin   of, 

71,  72. 
I'ltidff,  Ivan,  cited  on  Alaskan  volca- 

noi'H,  li70,  274. 
rctrniofjy,  brief  accrxint  of,  111-llH. 
I'liilippinu  InlandH,  Noiind  of  eruption 

of  Krakatoa  heard  at,  27. 
"  I'ine  tree  of  Vesuvius,"  brief  account 

of,  H,  IK. 
I'hiUH  M(intczum((,  n<enlloii  of,  17(1. 
I'inUH  ii.icudiistrohHS,  niciition  of,  170, 
I'iiiKx  Triiciite,  mention  of,  170. 
I'itt,  Mt.,  Ore.,  brief  account  of,  2:50  ; 

lifiRJit  of.  2:!4. 
riain  of  Leon,  character  of  country 

near,  1 18. 
I'linius.   GaiuH,   cited  on  eruption   of 

Vesuvius,  8,  14-10. 
Plutonic  plugs,  nature  and  origin  of, 

lOl-KKJ. 
I'lutonic  rocks,  definition  of,  Do. 
I'o^^uInnoi  volcano,  Alaska,  brief  ac- 
count of,  274. 
Pompeii,  reference  to  destruction  of,  10. 
Popocatepetl,    Mex.,    description    of, 

178-183  ;  heigiit  of,  174. 
Porphyritic  rocks,  term  cxplaini'd,  117. 
Port  of   Acheen,  Sumatra,    sound  of 

eruption  of  Krakatoa  heard  at,  27. 
Potential  plasticity  defined,  209. 
Powell,   J.    \V.,   cited  on   imbricated 

mountains,  84. 
Prestwich,  Joseph,  cited   on   volcanic 

theories,  308,  31U,  321,  324. 
Profiles  of  volcanic  mountains,  80-83. 
Pumice,  nature  and  origin  of,  04. 
Pyramid    Lake,    Xev.,   volcanic   dust 

near,  285,  290. 

Quartz  trachyte  (Hhyolite),  brief  ac- 
count of,  r22-124. 

Ragtown,  Nev.,  crater  near,  205-208. 
Ragtown  ponds,  Nev.,  description  of, 

205-208. 
Rainier,  Mt,  Wash.,  andesitic  rocks  in. 


126 ;  brief  account  of,  241-245 ;  height 
of,  234  ;  referenceH  to,  23.'t,  252. 

Katou  mesa,  Col.,  brief  account  of, 
203, 

Ueade,  T.  M.,  reference  to  works  of, 
.'L'l. 

Reclus,  fclisee,  cited  on  volcanoes  of 
Mexico,  1H;J;  references  to  book  by, 
17.3. 

Kliyolite,  brief  account  of,  122-124. 

Roiehtliofer,  F.  Maron,  reference  to, 252. 

IJockstock,  Kdwanl,  cited  on  eruption 
in  Lake  Iio[)ang(),  1  (7. 

Rocky  Mountains,  volcanoes  of,  257- 
207. 

Romero,  C.  M.,  cited  on  eruption  of 
(,'nnseguiiiii.  102. 

Rosenbusch,  II.,  reference  to  book  by, 
115. 

Russell,  I.  C,  cited  on  geology  of 
central  Washington,  257  ;  cited  r^n 
Mt.  St.  Klias,  208  ;  cited  on  pliitonic 
plugs,  102  ;  cited  on  Ragtown  ponds, 
Nev.,  208;  cited  on  subtubcrant 
mountains,  105 ;  citec'  on  trap  rocks 
of  the  Newark  system,  lol  ;  cited 
on  volcanic  dust  in  Alaska,  288 ; 
cited  on  volcanoes  of  Mono  Valley, 
Cal.,  225  ;  cited  on  volcanic  dust, 
285 ;  reference  to  ascent  of  Mt. 
Rainier  by,  245. 

Rutley,  Frank,  reference  and  book  by, 
115. 

Saddle  Mountain,  Ore.,  reference  to, 

257. 
"t.  Augustine,   Mt.,  Alaska,  mention 

of,  277 ;   description  of,   272,   273 ; 

reference  to,  81. 
St.  Elias,  Mt.,  Alaska,  not  a  volcano, 

208. 
St.  Helen's,  Mt.,  Wash.,  brief  accounts 

■jf,  2;]»,  240  ;  heiglits  of,  234  ;  re- 
cent eruption  of,  240  ;  reference  to, 

233. 
St.  Michael,  Alaska,  volcanoes  near, 

207. 
Salt  about  Vesuvius  after  an  eruption, 

22. 
Salt  Lake  City,  Utah,  volcanic  dust 

near,  280. 
Salt  on  Mt.  Etna,  53. 
San  Andres,  Mex.,  mention  of,  175. 


INI»KX 


34r> 


San   Kraiicisco   Mountain,    Ariz.,  df-      Staffa,  Isle  of,  Scotland,  refiicnct   to 

Hciiplioii  of,  102,  !(•:{.  '       roi'knof,  I'il. 

San  Salvador,  list  of  volcanoes  In,  \'.iH.      Stau'i  f  in  tlu!  liven  of  vulcaniitH,  J.')-lt*. 
Sand,  volcanic,  naturt>  and  niodu  of  |  Stalaftltfii  In  lava  tuniu  Is,  iiu>nti<in  of, 

occunenci'  of,  "'>,  7<l. 
8antr.  Catalina,  Mt.,MfX.,  UKiition  of, 

IIK). 
Santa  1m'  dc  Hoj^ota,  fall  of  volcanic 

dust  in.  Kill 
Santorln   vo|(;ur>,    nicntiun  of,  gatti-H 

Kiven  lift'  l»y,  .'il. 
Saiu-UH,  Mass,,  volcanic  tlust  from  near, 

•JIM). 
Scorlaceous  lava  ni  tlic  liasal  portions 

of  lava  Htrcains,  (itt-()M  ;  surfaces  of 

lava  streams,  (5.'{-(l(l. 
Scott,  .Mt.,  Ort'.,  liriulit  of,  2:)4. 
ScroiM',   (1.    1'.,  cited  on  vnlcanoeH  of 

Fraiicf,  1!);5. 
Sections  of  rocks,  liow  made,  116, 
Slialer,   X.   S.,   cited  on    eruption   of 

Vesnviu.s,  11,  12  ;  cited  on  orif,'in  of 

volcanoes,  ;)2.'!-;J2(l. 


Steam  liypotlieHes  of  the  orlniu  ot  vol- 

canouH,  '.i'2i),  '.I'M. 
Sieplii  ns,  .).  L.,  cited  on   eruption    if 

I/.alco,  San  Salvador,  111-11.'}. 
Steveiis,  Hazard,  ascent  of  .\!t.  Uainier 

i.y.  •-•12. 

Steveii.son,  J,  J.,  clcd  on  volcanoes  in 

New  .Mexico,  2ii;!-2t!."j. 
Stromltiili,  Italy,  de.seriptiou  cif,  2-7. 
Stroml)olian  sla^je  of  volcanoes  brietiy 

detlned,  11. 
Structure  of  volcanic  mountains,  bil- 

HM. 
Sulilinied  products  of  volcanoes,  J'i-.-,;{. 
Sulitulierant    nmuntaius,    natuie    and 

oriKin  of,  KHi-lo,'). 
Sunset   Hills,  Nev.,  reference  to  rocks 

of,  12.!. 


Shasta,  .Mt.,  C'al.,  andesitic  rocks  of,   i   Superior   Lalxc,   reference   to   iuneou.1 


125  ;  description  of,  225-228  ;  refer- 
ence  to,  252. 

Shastina,  Cal.,  reference  to,  227. 

Sheets,  intruded,  nature  and  origin  of, 
90-101. 

Shislialdin  volcano,  Alaska,  descrip- 
tion of,  274,  275  ;  prolile  of,  81. 

Siemens,  cited  on  gaseous  products 
of  volcanoes,  61. 

Sierra  Nevada  Mountains,  reference  to 
structure  of,  247. 

Sinj,'apore,  sound  of  eruption  of  Kra- 
katoa  heard  at,  27. 

Slag  of  furnjice,  resemblances  of,  to 
volcanic  rocks,  108. 

Snake  Uiver,  Wash.,  depth  of  canyon 
of,  251,  254,  250. 

Soda  lakes,  Nev.,  description  of,  205- 
208. 

Solfatara  .stage  in  volcanoes,  brief  ac- 
count of,  40. 

Somma,  Mt.,  Italy,  mention  of,  8,  13. 

Spanish  peaks.  Col.,  de.scription  of, 
259-262  ;  mention  of,  265. 

Squier,  E.  G.,  cited  on  eruption  of  Con- 
seguina,  Nicaragua,  159-161 ;  cited 
on  Izalco,  San  Salvador,  141 ;  cited 
on  young  volcano  in  Nicaragua,  140, 
148. 


rocks  of,  i;JO. 
Symons,  T.  W.,  cited  on  thickness  of 
Ct)lumbian  lava,  251. 

Tabernacle  crater,  Utah,  description  of, 

2l»2-205. 
Taylor,  .Mt.,  N.  M.,  description  of,  103- 

108. 
Tertiary  age  of  Columbia  lava,  253. 
Three  Sisters,  Ore.,  brief  account  of, 

2."><i,  2.^7;  mention  of,  2;i4. 
Tinteni,  N.  M,,  mention  of,  108. 
Tom,  .Mt.,  Mass.,  reference  to  rocks  of, 

121. 
Trachyte,  brief  account  of,  124. 
Trap  rocks  of  the  Newark  svstem,  4;)- 

45. 
Tres  Virgenes,  Me.x.,  mention  of,  100. 
Truckee  Canyon,  Nev.,  analysis  of  vol- 
canic dust  from,  202  ;  volcanic  dust 

in,  285-200. 
Tuff,  rhyolltic,  occurrence  of,  123. 
Tunnels  in  lava,  character  and  origin 

of,  58,  50. 
Tuxtla,  Max.,  description  of,  184,  1H5. 
Types  of  volcanoes  described,  1-45. 

Unalaska  Island,  Alaska,  volcanoes  on, 
281,282. 


B^i^ 


?TS53 


346 


INDEX 


Unimak  Island,  Alaska,  volcanoes  of. 

27;3-276. 
Union,  Mt.,  Ore.,  height  of,  2.'U. 
United  States,  volcanoes  of,  190-283. 
Utah,  volcanic  cniter  of,  198-205. 

Valmont,   Col.,   volcanic    cones  near, 

259. 
Vancouver, Capt.,  estimate  of  the  height 

of  Mt.  Hood  by,  238. 
Van  Hi.se,  C.  R.,  cited  on  cavities  in 

the  earth,  .309. 
Van  Trump,  1*.  B.,  ascent  of  Mt.Rainier 

by,  242. 
Vera  Cruz,  Mex.,  fall  of  volcanic  dust 

in,  1(50. 
Verbeek,  H.  D.  M.,  cited  on  eruption 

of  Ki-akatoa,  28. 
Vesuvian  stage  of  volcanoes,  briefly 

defined,  9. 
Vesuvius,  gases  given  off  by,  51  ;  de- 
scription of,  7-22 ;   mention   of,  1  ; 

structure  of,  illustrated,  87. 
Victoria  Plains,  Australia,  sound   of 

eruption  of  Krakatoa  heard  at,  27. 
Volcanic  bombs,  nature  and  origin  of, 


73,  74  ;  dust,  deposits  of,  284-296; 
rocks,  definition  of,  95  ;  necks,  men- 
tion of,  93  ;  necks,  nature  and  origin 
of,  89,  90. 

Washington,  deposits  of  volcanic  dust 

in,  287. 
Weathering,  nature  of,  91. 
Whymper,  E.,  cited  on  eruption  of 

dust  from  Cotopaxi,  77-79. 
Williams,  E.  H. ,  cited  on  andesite,  124 ; 

reference  to  book  by,  116. 
Wilson,  A.  D.,  ascent  of  Mt.  Rainier 

by,  242. 
Winchell,  W.  H.,  cited  on  volcanic 

dust,  289. 
Wrangell,  Mt.,  Alaska,  brief  account 

of,  269,  270. 

Xinantecatl,  Mex.,  description  of,  184. 

Yakima,  Wash.,  section  of  rocks  near, 

252,  253. 
Yemans,  H.  W.,  cited  on  Bogosloff,  278. 
Young  volcanoes,  descriptions  of,  139- 

166. 


/-VV 


mmm 


•9*' 


